Pattern 07 of 22

Sorting Pattern: Template + 401 LeetCode Problems

Spend O(n log n) once to buy an ordering that makes the rest of the problem trivial.

Easy: 80
Medium: 227
Hard: 94
Time: O(n log n)

What the sorting pattern is

Sorting is rarely the answer on its own; it is the setup that makes the answer obvious, and the skill being tested is choosing the key. Sorting intervals by start time puts every overlap next to its partner, so merging becomes one linear pass. Sorting by finishing time is what makes the greedy interval choice correct. Sorting an array before a two-pointer scan is what lets a comparison decide which pointer to move. Once the input is ordered, duplicates are adjacent, the median is at a known index, and binary search becomes available — three capabilities that between them dissolve a lot of problems. The cost is worth watching: O(n log n) is usually the cheap part next to whatever follows, but when the values are small integers, counting or bucket sort does it in linear time, and when only the kth element is wanted, quickselect gets it in expected linear time without sorting the rest. In Python the `key` argument, and tuples as keys for multi-level ordering, express nearly all of this without a comparator.

When to use it

Adjacency in sorted order is what makes the answer visible: overlaps, duplicates, closest pairs.
A greedy choice depends on processing items in a specific order.
Grouping is by a canonical form that sorting produces, such as sorted letters for anagrams.
Only the kth largest is needed and n is large — that is quickselect, not a full sort.
Values are bounded small integers, where counting sort beats the comparison lower bound.

The sorting template in Python

The shape, not a solution to any one problem. Adapt the condition and the summary being maintained; the skeleton stays the same across the 401 problems listed below.

PythonSorting template

def merge_intervals(intervals):
    intervals.sort(key=lambda pair: pair[0])   # sorting makes overlaps adjacent
    merged = []

    for start, finish in intervals:
        if merged and start <= merged[-1][1]:
            merged[-1][1] = max(merged[-1][1], finish)   # extend the open interval
        else:
            merged.append([start, finish])

    return merged

Complexity characteristics

Time: O(n log n)
Auxiliary space: O(n)for Python's Timsort

Comparison sorts cannot beat n log n, and that bound is usually the cheap part next to whatever the sorted order then enables. Two escapes exist when the input allows them: counting, bucket and radix sort run in linear time when the values are bounded small integers, and quickselect finds the kth element in expected O(n) without ordering the rest. Python's sort is stable and allocates a temporary buffer, so it costs O(n) space rather than the O(log n) an in-place quicksort would suggest.

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

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python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

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90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

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All 401 sorting LeetCode problems

Every problem in the library the sorting pattern applies to, grouped by LeetCode's own difficulty rating. 346 of the 401 carry a complete Python solution with a worked example and complexity analysis; the rest are listed for completeness, with the LeetCode Premium ones marked.

Easy (80)

Easy problems
No.	Problem	Topics
0088	Merge Sorted Array	Array, Two Pointers, Sorting
0169	Majority Element	Array, Hash Table, Divide and Conquer +2
0217	Contains Duplicate	Array, Hash Table, Sorting
0242	Valid Anagram	Hash Table, String, Sorting
0268	Missing Number	Bit Manipulation, Array, Hash Table +3
0349	Intersection of Two Arrays	Array, Hash Table, Two Pointers +2
0350	Intersection of Two Arrays II	Array, Hash Table, Two Pointers +2
0389	Find the Difference	Bit Manipulation, Hash Table, String +1
0414	Third Maximum Number	Array, Sorting
0455	Assign Cookies	Greedy, Array, Two Pointers +1
0506	Relative Ranks	Array, Sorting, Heap (Priority Queue)
0561	Array Partition	Greedy, Array, Counting Sort +1
0594	Longest Harmonious Subsequence	Array, Hash Table, Counting +2
0628	Maximum Product of Three Numbers	Array, Math, Sorting
0645	Set Mismatch	Bit Manipulation, Array, Hash Table +1
0747	Largest Number At Least Twice of Others	Array, Sorting
0252	Meeting RoomsPremium	Array, Sorting
0888	Fair Candy Swap	Array, Hash Table, Binary Search +1
0905	Sort Array By Parity	Array, Two Pointers, Sorting
0922	Sort Array By Parity II	Array, Two Pointers, Sorting
0976	Largest Perimeter Triangle	Greedy, Array, Math +1
0977	Squares of a Sorted Array	Array, Two Pointers, Sorting
1005	Maximize Sum Of Array After K Negations	Greedy, Array, Sorting
1030	Matrix Cells in Distance Order	Geometry, Array, Math +2
1051	Height Checker	Array, Counting Sort, Sorting
1065	Index Pairs of a StringPremium	Trie, Array, String +1
1086	High FivePremium	Array, Hash Table, Sorting +1
1099	Two Sum Less Than KPremium	Array, Two Pointers, Binary Search +1
1122	Relative Sort Array	Array, Hash Table, Counting Sort +1
1133	Largest Unique NumberPremium	Array, Hash Table, Sorting
1196	How Many Apples Can You Put into the BasketPremium	Greedy, Array, Sorting
1200	Minimum Absolute Difference	Array, Sorting
1331	Rank Transform of an Array	Array, Hash Table, Sorting
1337	The K Weakest Rows in a Matrix	Array, Binary Search, Matrix +2
1346	Check If N and Its Double Exist	Array, Hash Table, Two Pointers +2
1356	Sort Integers by The Number of 1 Bits	Bit Manipulation, Array, Counting +1
1365	How Many Numbers Are Smaller Than the Current Number	Array, Hash Table, Counting Sort +1
1385	Find the Distance Value Between Two Arrays	Array, Two Pointers, Binary Search +1
1403	Minimum Subsequence in Non-Increasing Order	Greedy, Array, Sorting
1460	Make Two Arrays Equal by Reversing Subarrays	Array, Hash Table, Sorting
1464	Maximum Product of Two Elements in an Array	Array, Sorting, Heap (Priority Queue)
1491	Average Salary Excluding the Minimum and Maximum Salary	Array, Sorting
1502	Can Make Arithmetic Progression From Sequence	Array, Sorting
1608	Special Array With X Elements Greater Than or Equal X	Array, Binary Search, Sorting
1619	Mean of Array After Removing Some Elements	Array, Sorting
1636	Sort Array by Increasing Frequency	Array, Hash Table, Sorting
1637	Widest Vertical Area Between Two Points Containing No Points	Array, Sorting
1710	Maximum Units on a Truck	Greedy, Array, Sorting
1859	Sorting the Sentence	String, Sorting
1913	Maximum Product Difference Between Two Pairs	Array, Sorting
1984	Minimum Difference Between Highest and Lowest of K Scores	Array, Sorting, Sliding Window
2037	Minimum Number of Moves to Seat Everyone	Greedy, Array, Counting Sort +1
2089	Find Target Indices After Sorting Array	Array, Binary Search, Sorting
2094	Finding 3-Digit Even Numbers	Recursion, Array, Hash Table +2
2099	Find Subsequence of Length K With the Largest Sum	Array, Hash Table, Sorting +1
2144	Minimum Cost of Buying Candies With Discount	Greedy, Array, Sorting
2148	Count Elements With Strictly Smaller and Greater Elements	Array, Counting, Sorting
2154	Keep Multiplying Found Values by Two	Array, Hash Table, Sorting +1
2160	Minimum Sum of Four Digit Number After Splitting Digits	Greedy, Math, Sorting
2164	Sort Even and Odd Indices Independently	Array, Sorting
2229	Check if an Array Is ConsecutivePremium	Array, Hash Table, Sorting
2231	Largest Number After Digit Swaps by Parity	Sorting, Heap (Priority Queue)
2248	Intersection of Multiple Arrays	Array, Hash Table, Counting +1
2273	Find Resultant Array After Removing Anagrams	Array, Hash Table, String +1
2335	Minimum Amount of Time to Fill Cups	Greedy, Array, Sorting +1
2357	Make Array Zero by Subtracting Equal Amounts	Greedy, Array, Hash Table +3
2363	Merge Similar Items	Array, Hash Table, Ordered Set +1
2389	Longest Subsequence With Limited Sum	Greedy, Array, Binary Search +2
2418	Sort the People	Array, Hash Table, String +1
2441	Largest Positive Integer That Exists With Its Negative	Array, Hash Table, Two Pointers +1
2465	Number of Distinct Averages	Array, Hash Table, Two Pointers +1
2475	Number of Unequal Triplets in Array	Array, Hash Table, Sorting
2500	Delete Greatest Value in Each Row	Array, Matrix, Sorting +2
2578	Split With Minimum Sum	Greedy, Math, Sorting
2706	Buy Two Chocolates	Greedy, Array, Sorting
2733	Neither Minimum nor Maximum	Array, Sorting
2784	Check if Array is Good	Array, Hash Table, Sorting
2824	Count Pairs Whose Sum is Less than Target	Array, Two Pointers, Binary Search +1
2974	Minimum Number Game	Array, Sorting, Simulation +1
2996	Smallest Missing Integer Greater Than Sequential Prefix Sum	Array, Hash Table, Sorting

Medium (227)

Medium problems
No.	Problem	Topics
0015	3Sum	Array, Two Pointers, Sorting
0016	3Sum Closest	Array, Two Pointers, Sorting
0018	4Sum	Array, Two Pointers, Sorting
0047	Permutations II	Array, Backtracking, Sorting
0049	Group Anagrams	Array, Hash Table, String +1
0056	Merge Intervals	Array, Sorting
0075	Sort Colors	Array, Two Pointers, Sorting
0147	Insertion Sort List	Linked List, Sorting
0148	Sort List	Linked List, Two Pointers, Divide and Conquer +2
0164	Maximum Gap	Array, Bucket Sort, Radix Sort +1
0179	Largest Number	Greedy, Array, String +1
0215	Kth Largest Element in an Array	Array, Divide and Conquer, Quickselect +2
0229	Majority Element II	Array, Hash Table, Counting +1
0274	H-Index	Array, Counting Sort, Sorting
0324	Wiggle Sort II	Greedy, Array, Divide and Conquer +2
0347	Top K Frequent Elements	Array, Hash Table, Divide and Conquer +5
0368	Largest Divisible Subset	Array, Math, Dynamic Programming +1
0378	Kth Smallest Element in a Sorted Matrix	Array, Binary Search, Matrix +2
0406	Queue Reconstruction by Height	Binary Indexed Tree, Segment Tree, Array +1
0435	Non-overlapping Intervals	Greedy, Array, Dynamic Programming +1
0436	Find Right Interval	Array, Binary Search, Sorting
0442	Find All Duplicates in an Array	Array, Hash Table, Sorting
0451	Sort Characters By Frequency	Hash Table, String, Bucket Sort +3
0452	Minimum Number of Arrows to Burst Balloons	Greedy, Array, Sorting
0462	Minimum Moves to Equal Array Elements II	Array, Math, Sorting
0475	Heaters	Array, Two Pointers, Binary Search +1
0522	Longest Uncommon Subsequence II	Array, Hash Table, Two Pointers +2
0524	Longest Word in Dictionary through Deleting	Array, Two Pointers, String +1
0532	K-diff Pairs in an Array	Array, Hash Table, Two Pointers +2
0539	Minimum Time Difference	Array, Math, String +1
0581	Shortest Unsorted Continuous Subarray	Stack, Greedy, Array +3
0611	Valid Triangle Number	Greedy, Array, Two Pointers +2
0621	Task Scheduler	Greedy, Array, Hash Table +3
0646	Maximum Length of Pair Chain	Greedy, Array, Dynamic Programming +1
0658	Find K Closest Elements	Array, Two Pointers, Binary Search +3
0692	Top K Frequent Words	Trie, Array, Hash Table +5
0720	Longest Word in Dictionary	Trie, Array, Hash Table +2
0721	Accounts Merge	Depth-First Search, Breadth-First Search, Union Find +4
0846	Hand of Straights	Greedy, Array, Hash Table +1
0853	Car Fleet	Stack, Array, Sorting +1
0973	K Closest Points to Origin	Geometry, Array, Math +4
1268	Search Suggestions System	Trie, Array, String +3
1657	Determine if Two Strings Are Close	Hash Table, String, Counting +1
1679	Max Number of K-Sum Pairs	Array, Hash Table, Two Pointers +1
2300	Successful Pairs of Spells and Potions	Array, Two Pointers, Binary Search +1
2542	Maximum Subsequence Score	Greedy, Array, Sorting +1
0253	Meeting Rooms IIPremium	Greedy, Array, Two Pointers +3
0259	3Sum SmallerPremium	Array, Two Pointers, Binary Search +1
0280	Wiggle SortPremium	Greedy, Array, Sorting
0314	Binary Tree Vertical Order TraversalPremium	Tree, Depth-First Search, Breadth-First Search +3
0360	Sort Transformed ArrayPremium	Array, Math, Two Pointers +1
0767	Reorganize String	Greedy, Hash Table, String +3
0769	Max Chunks To Make Sorted	Stack, Greedy, Array +2
0786	K-th Smallest Prime Fraction	Array, Two Pointers, Binary Search +2
0791	Custom Sort String	Hash Table, String, Sorting
0792	Number of Matching Subsequences	Trie, Array, Hash Table +4
0823	Binary Trees With Factors	Array, Hash Table, Dynamic Programming +1
0825	Friends Of Appropriate Ages	Array, Two Pointers, Binary Search +1
0826	Most Profit Assigning Work	Greedy, Array, Two Pointers +2
0833	Find And Replace in String	Array, Hash Table, String +1
0869	Reordered Power of 2	Hash Table, Math, Counting +2
0870	Advantage Shuffle	Greedy, Array, Two Pointers +1
0881	Boats to Save People	Greedy, Array, Two Pointers +1
0893	Groups of Special-Equivalent Strings	Array, Hash Table, String +1
0910	Smallest Range II	Greedy, Array, Math +1
0912	Sort an Array	Array, Divide and Conquer, Bucket Sort +5
0923	3Sum With Multiplicity	Array, Hash Table, Two Pointers +2
0937	Reorder Data in Log Files	Array, String, Sorting
0939	Minimum Area Rectangle	Geometry, Array, Hash Table +2
0945	Minimum Increment to Make Array Unique	Greedy, Array, Counting +1
0948	Bag of Tokens	Greedy, Array, Two Pointers +1
0950	Reveal Cards In Increasing Order	Queue, Array, Sorting +1
0954	Array of Doubled Pairs	Greedy, Array, Hash Table +1
0969	Pancake Sorting	Greedy, Array, Two Pointers +1
1029	Two City Scheduling	Greedy, Array, Sorting
1040	Moving Stones Until Consecutive II	Array, Math, Sorting +1
1048	Longest String Chain	Array, Hash Table, Two Pointers +3
1054	Distant Barcodes	Greedy, Array, Hash Table +3
1057	Campus BikesPremium	Array, Sorting, Heap (Priority Queue)
1058	Minimize Rounding Error to Meet TargetPremium	Greedy, Array, Math +2
1087	Brace ExpansionPremium	Stack, Breadth-First Search, String +2
1090	Largest Values From Labels	Greedy, Array, Hash Table +2
1094	Car Pooling	Array, Prefix Sum, Sorting +2
1101	The Earliest Moment When Everyone Become FriendsPremium	Union Find, Array, Sorting
1152	Analyze User Website Visit PatternPremium	Array, Hash Table, String +1
1169	Invalid Transactions	Array, Hash Table, String +1
1170	Compare Strings by Frequency of the Smallest Character	Array, Hash Table, String +2
1181	Before and After PuzzlePremium	Array, Hash Table, String +1
1202	Smallest String With Swaps	Depth-First Search, Breadth-First Search, Union Find +4
1229	Meeting SchedulerPremium	Array, Two Pointers, Sorting
1244	Design A LeaderboardPremium	Design, Hash Table, Sorting
1262	Greatest Sum Divisible by Three	Greedy, Array, Dynamic Programming +1
1288	Remove Covered Intervals	Array, Sorting
1296	Divide Array in Sets of K Consecutive Numbers	Greedy, Array, Hash Table +1
1300	Sum of Mutated Array Closest to Target	Array, Binary Search, Sorting
1305	All Elements in Two Binary Search Trees	Tree, Depth-First Search, Binary Search Tree +2
1311	Get Watched Videos by Your Friends	Breadth-First Search, Graph, Array +2
1329	Sort the Matrix Diagonally	Array, Matrix, Sorting
1333	Filter Restaurants by Vegan-Friendly, Price and Distance	Array, Sorting
1338	Reduce Array Size to The Half	Greedy, Array, Hash Table +2
1348	Tweet Counts Per Frequency	Design, Hash Table, String +3
1353	Maximum Number of Events That Can Be Attended	Greedy, Array, Sorting +1
1366	Rank Teams by Votes	Array, Hash Table, String +2
1387	Sort Integers by The Power Value	Memoization, Dynamic Programming, Sorting
1418	Display Table of Food Orders in a Restaurant	Array, Hash Table, String +2
1424	Diagonal Traverse II	Array, Sorting, Heap (Priority Queue)
1433	Check If a String Can Break Another String	Greedy, String, Sorting
1451	Rearrange Words in a Sentence	String, Sorting
1465	Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts	Greedy, Array, Sorting
1471	The k Strongest Values in an Array	Array, Two Pointers, Sorting
1481	Least Number of Unique Integers after K Removals	Greedy, Array, Hash Table +2
1498	Number of Subsequences That Satisfy the Given Sum Condition	Array, Two Pointers, Binary Search +1
1500	Design a File Sharing SystemPremium	Design, Hash Table, Data Stream +2
1508	Range Sum of Sorted Subarray Sums	Array, Two Pointers, Binary Search +2
1509	Minimum Difference Between Largest and Smallest Value in Three Moves	Greedy, Array, Sorting
1552	Magnetic Force Between Two Balls	Array, Binary Search, Sorting
1561	Maximum Number of Coins You Can Get	Greedy, Array, Math +2
1564	Put Boxes Into the Warehouse IPremium	Greedy, Array, Sorting
1580	Put Boxes Into the Warehouse IIPremium	Greedy, Array, Sorting
1589	Maximum Sum Obtained of Any Permutation	Greedy, Array, Prefix Sum +1
1604	Alert Using Same Key-Card Three or More Times in a One Hour Period	Array, Hash Table, String +1
1626	Best Team With No Conflicts	Array, Dynamic Programming, Sorting
1630	Arithmetic Subarrays	Array, Hash Table, Sorting
1647	Minimum Deletions to Make Character Frequencies Unique	Greedy, Hash Table, String +1
1648	Sell Diminishing-Valued Colored Balls	Greedy, Array, Math +3
1686	Stone Game VI	Greedy, Array, Math +3
1727	Largest Submatrix With Rearrangements	Greedy, Array, Matrix +1
1738	Find Kth Largest XOR Coordinate Value	Bit Manipulation, Array, Divide and Conquer +5
1772	Sort Features by PopularityPremium	Array, Hash Table, String +1
1798	Maximum Number of Consecutive Values You Can Make	Greedy, Array, Sorting
1818	Minimum Absolute Sum Difference	Array, Binary Search, Ordered Set +1
1833	Maximum Ice Cream Bars	Greedy, Array, Counting Sort +1
1834	Single-Threaded CPU	Array, Sorting, Heap (Priority Queue)
1838	Frequency of the Most Frequent Element	Greedy, Array, Binary Search +3
1846	Maximum Element After Decreasing and Rearranging	Greedy, Array, Sorting
1874	Minimize Product Sum of Two ArraysPremium	Greedy, Array, Sorting
1877	Minimize Maximum Pair Sum in Array	Greedy, Array, Two Pointers +1
1878	Get Biggest Three Rhombus Sums in a Grid	Array, Math, Matrix +3
1885	Count Pairs in Two ArraysPremium	Array, Two Pointers, Binary Search +1
1887	Reduction Operations to Make the Array Elements Equal	Array, Sorting
1921	Eliminate Maximum Number of Monsters	Greedy, Array, Sorting
1943	Describe the Painting	Array, Hash Table, Prefix Sum +1
1968	Array With Elements Not Equal to Average of Neighbors	Greedy, Array, Sorting
1985	Find the Kth Largest Integer in the Array	Array, String, Divide and Conquer +3
1996	The Number of Weak Characters in the Game	Stack, Greedy, Array +2
2007	Find Original Array From Doubled Array	Greedy, Array, Hash Table +1
2008	Maximum Earnings From Taxi	Array, Hash Table, Binary Search +2
2015	Average Height of Buildings in Each SegmentPremium	Greedy, Array, Sorting +1
2021	Brightest Position on StreetPremium	Array, Ordered Set, Prefix Sum +1
2031	Count Subarrays With More Ones Than ZerosPremium	Binary Indexed Tree, Segment Tree, Array +5
2033	Minimum Operations to Make a Uni-Value Grid	Array, Math, Matrix +1
2046	Sort Linked List Already Sorted Using Absolute ValuesPremium	Linked List, Two Pointers, Sorting
2054	Two Best Non-Overlapping Events	Array, Binary Search, Dynamic Programming +2
2070	Most Beautiful Item for Each Query	Array, Binary Search, Sorting
2098	Subsequence of Size K With the Largest Even SumPremium	Greedy, Array, Sorting
2126	Destroying Asteroids	Greedy, Array, Sorting
2135	Count Words Obtained After Adding a Letter	Bit Manipulation, Array, Hash Table +2
2146	K Highest Ranked Items Within a Price Range	Breadth-First Search, Array, Matrix +2
2165	Smallest Value of the Rearranged Number	Math, Sorting
2171	Removing Minimum Number of Magic Beans	Greedy, Array, Enumeration +2
2191	Sort the Jumbled Numbers	Array, Sorting
2195	Append K Integers With Minimal Sum	Greedy, Array, Math +1
2225	Find Players With Zero or One Losses	Array, Hash Table, Counting +1
2250	Count Number of Rectangles Containing Each Point	Binary Indexed Tree, Array, Hash Table +2
2268	Minimum Number of KeypressesPremium	Greedy, Hash Table, String +2
2271	Maximum White Tiles Covered by a Carpet	Greedy, Array, Binary Search +3
2274	Maximum Consecutive Floors Without Special Floors	Array, Sorting
2279	Maximum Bags With Full Capacity of Rocks	Greedy, Array, Sorting
2280	Minimum Lines to Represent a Line Chart	Geometry, Array, Math +2
2285	Maximum Total Importance of Roads	Greedy, Graph, Sorting +1
2294	Partition Array Such That Maximum Difference Is K	Greedy, Array, Sorting
2323	Find Minimum Time to Finish All Jobs IIPremium	Greedy, Array, Sorting
2332	The Latest Time to Catch a Bus	Array, Two Pointers, Binary Search +1
2333	Minimum Sum of Squared Difference	Greedy, Array, Binary Search +2
2342	Max Sum of a Pair With Equal Sum of Digits	Array, Hash Table, Sorting +1
2343	Query Kth Smallest Trimmed Number	Array, String, Divide and Conquer +4
2345	Finding the Number of Visible MountainsPremium	Stack, Array, Sorting +1
2406	Divide Intervals Into Minimum Number of Groups	Greedy, Array, Two Pointers +3
2410	Maximum Matching of Players With Trainers	Greedy, Array, Two Pointers +1
2456	Most Popular Video Creator	Array, Hash Table, String +2
2491	Divide Players Into Teams of Equal Skill	Array, Hash Table, Two Pointers +1
2497	Maximum Star Sum of a Graph	Greedy, Graph, Array +2
2501	Longest Square Streak in an Array	Array, Hash Table, Binary Search +2
2512	Reward Top K Students	Array, Hash Table, String +2
2517	Maximum Tastiness of Candy Basket	Greedy, Array, Binary Search +1
2545	Sort the Students by Their Kth Score	Array, Matrix, Sorting
2548	Maximum Price to Fill a BagPremium	Greedy, Array, Sorting
2554	Maximum Number of Integers to Choose From a Range I	Greedy, Array, Hash Table +2
2557	Maximum Number of Integers to Choose From a Range IIPremium	Greedy, Array, Binary Search +1
2563	Count the Number of Fair Pairs	Array, Two Pointers, Binary Search +1
2567	Minimum Score by Changing Two Elements	Greedy, Array, Sorting
2576	Find the Maximum Number of Marked Indices	Greedy, Array, Two Pointers +2
2580	Count Ways to Group Overlapping Ranges	Array, Sorting
2583	Kth Largest Sum in a Binary Tree	Tree, Breadth-First Search, Binary Tree +1
2587	Rearrange Array to Maximize Prefix Score	Greedy, Array, Prefix Sum +1
2590	Design a Todo ListPremium	Design, Array, Hash Table +2
2592	Maximize Greatness of an Array	Greedy, Array, Two Pointers +1
2593	Find Score of an Array After Marking All Elements	Array, Hash Table, Sorting +2
2597	The Number of Beautiful Subsets	Array, Hash Table, Math +4
2602	Minimum Operations to Make All Array Elements Equal	Array, Binary Search, Prefix Sum +1
2607	Make K-Subarray Sums Equal	Greedy, Array, Math +2
2611	Mice and Cheese	Greedy, Array, Sorting +1
2616	Minimize the Maximum Difference of Pairs	Greedy, Array, Binary Search +2
2638	Count the Number of K-Free SubsetsPremium	Array, Math, Dynamic Programming +2
2655	Find Maximal Uncovered RangesPremium	Array, Sorting
2679	Sum in a Matrix	Array, Matrix, Sorting +2
2708	Maximum Strength of a Group	Greedy, Bit Manipulation, Array +4
2731	Movement of Robots	Brainteaser, Array, Prefix Sum +1
2740	Find the Value of the Partition	Array, Sorting
2747	Count Zero Request Servers	Array, Hash Table, Sorting +1
2766	Relocate Marbles	Array, Hash Table, Sorting +1
2779	Maximum Beauty of an Array After Applying Operation	Array, Binary Search, Sorting +1
2780	Minimum Index of a Valid Split	Array, Hash Table, Sorting
2785	Sort Vowels in a String	String, Sorting
2830	Maximize the Profit as the Salesman	Array, Hash Table, Binary Search +2
2838	Maximum Coins Heroes Can CollectPremium	Array, Two Pointers, Binary Search +2
2840	Check if Strings Can be Made Equal With Operations II	Hash Table, String, Sorting
2860	Happy Students	Array, Enumeration, Sorting
2863	Maximum Length of Semi-Decreasing SubarraysPremium	Stack, Array, Sorting +1
2895	Minimum Processing Time	Greedy, Array, Sorting
2933	High-Access Employees	Array, Hash Table, String +1
2943	Maximize Area of Square Hole in Grid	Array, Sorting
2948	Make Lexicographically Smallest Array by Swapping Elements	Union Find, Array, Sorting
2952	Minimum Number of Coins to be Added	Greedy, Array, Sorting
2966	Divide Array Into Arrays With Max Difference	Greedy, Array, Sorting
2967	Minimum Cost to Make Array Equalindromic	Greedy, Array, Math +2
2971	Find Polygon With the Largest Perimeter	Greedy, Array, Prefix Sum +1

Hard (94)

Hard problems
No.	Problem	Topics
0023	Merge k Sorted Lists	Linked List, Divide and Conquer, Heap (Priority Queue) +1
0218	The Skyline Problem	Binary Indexed Tree, Segment Tree, Array +5
0220	Contains Duplicate III	Array, Bucket Sort, Ordered Set +2
0295	Find Median from Data Stream	Design, Two Pointers, Data Stream +2
0315	Count of Smaller Numbers After Self	Binary Indexed Tree, Segment Tree, Array +4
0327	Count of Range Sum	Binary Indexed Tree, Segment Tree, Array +4
0354	Russian Doll Envelopes	Array, Binary Search, Dynamic Programming +1
0472	Concatenated Words	Depth-First Search, Trie, Array +3
0493	Reverse Pairs	Binary Indexed Tree, Segment Tree, Array +4
0502	IPO	Greedy, Array, Sorting +1
0630	Course Schedule III	Greedy, Array, Sorting +1
0632	Smallest Range Covering Elements from K Lists	Greedy, Array, Hash Table +3
0710	Random Pick with Blacklist	Array, Hash Table, Math +3
0719	Find K-th Smallest Pair Distance	Array, Two Pointers, Binary Search +1
1235	Maximum Profit in Job Scheduling	Array, Binary Search, Dynamic Programming +1
1851	Minimum Interval to Include Each Query	Array, Binary Search, Sorting +2
0296	Best Meeting PointPremium	Array, Math, Matrix +1
0358	Rearrange String k Distance ApartPremium	Greedy, Hash Table, String +3
0527	Word AbbreviationPremium	Greedy, Trie, Array +2
0588	Design In-Memory File SystemPremium	Design, Trie, Hash Table +2
0642	Design Search Autocomplete SystemPremium	Depth-First Search, Design, Trie +4
0726	Number of Atoms	Stack, Hash Table, String +1
0757	Set Intersection Size At Least Two	Greedy, Array, Sorting
0759	Employee Free TimePremium	Array, Sorting, Line Sweep +1
0768	Max Chunks To Make Sorted II	Stack, Greedy, Array +2
0857	Minimum Cost to Hire K Workers	Greedy, Array, Sorting +1
0891	Sum of Subsequence Widths	Array, Math, Sorting
0899	Orderly Queue	Math, String, Sorting
0975	Odd Even Jump	Stack, Array, Dynamic Programming +3
0987	Vertical Order Traversal of a Binary Tree	Tree, Depth-First Search, Breadth-First Search +3
1096	Brace Expansion II	Stack, Breadth-First Search, Hash Table +3
1183	Maximum Number of OnesPremium	Greedy, Math, Sorting +1
1187	Make Array Strictly Increasing	Array, Binary Search, Dynamic Programming +1
1340	Jump Game V	Array, Dynamic Programming, Sorting
1363	Largest Multiple of Three	Greedy, Array, Math +2
1383	Maximum Performance of a Team	Greedy, Array, Sorting +1
1402	Reducing Dishes	Greedy, Array, Dynamic Programming +1
1478	Allocate Mailboxes	Array, Math, Dynamic Programming +1
1489	Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree	Union Find, Graph, Minimum Spanning Tree +2
1547	Minimum Cost to Cut a Stick	Array, Dynamic Programming, Sorting
1585	Check If String Is Transformable With Substring Sort Operations	Greedy, String, Sorting
1610	Maximum Number of Visible Points	Geometry, Array, Math +2
1632	Rank Transform of a Matrix	Union Find, Graph, Topological Sort +3
1649	Create Sorted Array through Instructions	Binary Indexed Tree, Segment Tree, Array +4
1665	Minimum Initial Energy to Finish Tasks	Greedy, Array, Sorting
1691	Maximum Height by Stacking Cuboids	Array, Dynamic Programming, Sorting
1697	Checking Existence of Edge Length Limited Paths	Union Find, Graph, Array +2
1751	Maximum Number of Events That Can Be Attended II	Array, Binary Search, Dynamic Programming +1
1755	Closest Subsequence Sum	Bit Manipulation, Array, Two Pointers +3
1782	Count Pairs Of Nodes	Graph, Array, Hash Table +4
1840	Maximum Building Height	Array, Math, Sorting
1847	Closest Room	Array, Binary Search, Ordered Set +1
1889	Minimum Space Wasted From Packaging	Array, Binary Search, Prefix Sum +1
1998	GCD Sort of an Array	Union Find, Array, Math +2
2071	Maximum Number of Tasks You Can Assign	Greedy, Queue, Array +4
2092	Find All People With Secret	Depth-First Search, Breadth-First Search, Union Find +2
2122	Recover the Original Array	Array, Hash Table, Two Pointers +2
2136	Earliest Possible Day of Full Bloom	Greedy, Array, Sorting
2141	Maximum Running Time of N Computers	Greedy, Array, Binary Search +1
2179	Count Good Triplets in an Array	Binary Indexed Tree, Segment Tree, Array +4
2234	Maximum Total Beauty of the Gardens	Greedy, Array, Two Pointers +4
2242	Maximum Score of a Node Sequence	Graph, Array, Enumeration +1
2251	Number of Flowers in Full Bloom	Array, Hash Table, Binary Search +3
2344	Minimum Deletions to Make Array Divisible	Array, Math, Number Theory +2
2371	Minimize Maximum Value in a GridPremium	Union Find, Graph, Topological Sort +3
2386	Find the K-Sum of an Array	Array, Sorting, Heap (Priority Queue)
2402	Meeting Rooms III	Array, Hash Table, Sorting +2
2412	Minimum Money Required Before Transactions	Greedy, Array, Sorting
2421	Number of Good Paths	Tree, Union Find, Graph +3
2426	Number of Pairs Satisfying Inequality	Binary Indexed Tree, Segment Tree, Array +4
2448	Minimum Cost to Make Array Equal	Greedy, Array, Binary Search +2
2449	Minimum Number of Operations to Make Arrays Similar	Greedy, Array, Sorting
2454	Next Greater Element IV	Stack, Array, Binary Search +3
2459	Sort Array by Moving Items to Empty SpacePremium	Greedy, Array, Sorting
2463	Minimum Total Distance Traveled	Array, Dynamic Programming, Sorting
2503	Maximum Number of Points From Grid Queries	Breadth-First Search, Union Find, Array +4
2519	Count the Number of K-Big IndicesPremium	Binary Indexed Tree, Segment Tree, Array +4
2551	Put Marbles in Bags	Greedy, Array, Sorting +1
2589	Minimum Time to Complete All Tasks	Stack, Greedy, Array +2
2604	Minimum Time to Eat All GrainsPremium	Array, Two Pointers, Binary Search +1
2613	Beautiful PairsPremium	Geometry, Array, Math +3
2659	Make Array Empty	Greedy, Binary Indexed Tree, Segment Tree +4
2681	Power of Heroes	Array, Math, Dynamic Programming +2
2713	Maximum Strictly Increasing Cells in a Matrix	Memoization, Array, Hash Table +5
2736	Maximum Sum Queries	Stack, Binary Indexed Tree, Segment Tree +4
2751	Robot Collisions	Stack, Array, Sorting +1
2790	Maximum Number of Groups With Increasing Length	Greedy, Array, Math +2
2809	Minimum Time to Make Array Sum At Most x	Array, Dynamic Programming, Sorting
2813	Maximum Elegance of a K-Length Subsequence	Stack, Greedy, Array +3
2818	Apply Operations to Maximize Score	Stack, Greedy, Array +4
2819	Minimum Relative Loss After Buying ChocolatesPremium	Array, Binary Search, Prefix Sum +1
2931	Maximum Spending After Buying Items	Greedy, Array, Matrix +2
2968	Apply Operations to Maximize Frequency Score	Array, Binary Search, Prefix Sum +2
2973	Find Number of Coins to Place in Tree Nodes	Tree, Depth-First Search, Dynamic Programming +2

Sorting pattern FAQ

What is the sorting pattern?

How many LeetCode problems use the sorting pattern?

This page lists 401 LeetCode problems that the sorting pattern applies to: 80 Easy, 227 Medium and 94 Hard. 346 of them carry a complete Python solution with complexity analysis.

What is the time complexity of the sorting pattern?

O(n log n) time and O(n) for Python's Timsort space. Comparison sorts cannot beat n log n, and that bound is usually the cheap part next to whatever the sorted order then enables. Two escapes exist when the input allows them: counting, bucket and radix sort run in linear time when the values are bounded small integers, and quickselect finds the kth element in expected O(n) without ordering the rest. Python's sort is stable and allocates a temporary buffer, so it costs O(n) space rather than the O(log n) an in-place quicksort would suggest.

When should I use the sorting pattern in an interview?

Adjacency in sorted order is what makes the answer visible: overlaps, duplicates, closest pairs. A greedy choice depends on processing items in a specific order.

Which sorting problem should I start with?

LeetCode 88. Merge Sorted Array is the lowest-numbered Easy problem on this page, which makes it the usual starting point: the technique is visible without the problem's own complications getting in the way.

What patterns are related to sorting?

Greedy, Two Pointers, Binary Search, Heap / Priority Queue. Problems frequently sit in more than one of these, and the overlap is where the interesting follow-up questions come from.

More ways in: all 22 patterns, the curated study lists, or the full problem list.

What the sorting pattern is

When to use it

The sorting template in Python

Complexity characteristics

Meet the sorting problem you did not practise.

Approach

Approach

Approach

All 401 sorting LeetCode problems

Easy (80)80

Medium (227)227

Hard (94)94

Related patterns

Sorting pattern FAQ

What is the sorting pattern?

How many LeetCode problems use the sorting pattern?

What is the time complexity of the sorting pattern?

When should I use the sorting pattern in an interview?

Which sorting problem should I start with?

What patterns are related to sorting?

Easy (80)

Medium (227)

Hard (94)