Enumeration LeetCode Problems: All 80,
With Python Solutions

Every problem in this library that LeetCode tags Enumeration. 75 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

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Easy: 20
Medium: 40
Hard: 20

Enumeration problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (20)

Easy problems
No.	Problem	Topics
1534	Count Good Triplets	Array, Enumeration
1566	Detect Pattern of Length M Repeated K or More Times	Array, Enumeration
1863	Sum of All Subset XOR Totals	Bit Manipulation, Array, Math +3
1925	Count Square Sum Triples	Math, Enumeration
1952	Three Divisors	Math, Enumeration, Number Theory
1995	Count Special Quadruplets	Array, Hash Table, Enumeration
2094	Finding 3-Digit Even Numbers	Recursion, Array, Hash Table +2
2259	Remove Digit From Number to Maximize Result	Greedy, String, Enumeration
2309	Greatest English Letter in Upper and Lower Case	Hash Table, String, Enumeration
2367	Number of Arithmetic Triplets	Array, Hash Table, Two Pointers +1
2427	Number of Common Factors	Math, Enumeration, Number Theory
2437	Number of Valid Clock Times	String, Enumeration
2605	Form Smallest Number From Two Digit Arrays	Array, Hash Table, Enumeration
2765	Longest Alternating Subarray	Array, Enumeration
2778	Sum of Squares of Special Elements	Array, Enumeration
2843	Count Symmetric Integers	Math, Enumeration
2928	Distribute Candies Among Children I	Math, Combinatorics, Enumeration
2951	Find the Peaks	Array, Enumeration
2970	Count the Number of Incremovable Subarrays I	Array, Two Pointers, Binary Search +1
0800	Similar RGB ColorPremium	Math, String, Enumeration

Medium (40)

Medium problems
No.	Problem	Topics
0204	Count Primes	Array, Math, Enumeration +1
0816	Ambiguous Coordinates	String, Backtracking, Enumeration
0845	Longest Mountain in Array	Array, Two Pointers, Dynamic Programming +1
0869	Reordered Power of 2	Hash Table, Math, Counting +2
0949	Largest Time for Given Digits	Array, String, Backtracking +1
0970	Powerful Integers	Hash Table, Math, Enumeration
1291	Sequential Digits	Enumeration
1620	Coordinate With Maximum Network Quality	Array, Enumeration
1625	Lexicographically Smallest String After Applying Operations	Depth-First Search, Breadth-First Search, String +1
1638	Count Substrings That Differ by One Character	Hash Table, String, Dynamic Programming +1
1849	Splitting a String Into Descending Consecutive Values	String, Backtracking, Enumeration
1958	Check if Move is Legal	Array, Enumeration, Matrix
2018	Check if Word Can Be Placed In Crossword	Array, Enumeration, Matrix
2044	Count Number of Maximum Bitwise-OR Subsets	Bit Manipulation, Array, Backtracking +1
2048	Next Greater Numerically Balanced Number	Hash Table, Math, Backtracking +2
2162	Minimum Cost to Set Cooking Time	Math, Enumeration
2171	Removing Minimum Number of Magic Beans	Greedy, Array, Enumeration +2
2212	Maximum Points in an Archery Competition	Bit Manipulation, Array, Backtracking +1
2232	Minimize Result by Adding Parentheses to Expression	String, Enumeration
2240	Number of Ways to Buy Pens and Pencils	Math, Enumeration
2249	Count Lattice Points Inside a Circle	Geometry, Array, Hash Table +2
2261	K Divisible Elements Subarrays	Trie, Array, Hash Table +3
2310	Sum of Numbers With Units Digit K	Greedy, Math, Dynamic Programming +1
2397	Maximum Rows Covered by Columns	Bit Manipulation, Array, Backtracking +2
2443	Sum of Number and Its Reverse	Math, Enumeration
2708	Maximum Strength of a Group	Greedy, Bit Manipulation, Array +4
2735	Collecting Chocolates	Array, Enumeration
2749	Minimum Operations to Make the Integer Zero	Bit Manipulation, Brainteaser, Enumeration
2761	Prime Pairs With Target Sum	Array, Math, Enumeration +1
2768	Number of Black Blocks	Array, Hash Table, Enumeration
2800	Shortest String That Contains Three Strings	Greedy, String, Enumeration
2844	Minimum Operations to Make a Special Number	Greedy, Math, String +1
2860	Happy Students	Array, Enumeration, Sorting
2929	Distribute Candies Among Children II	Math, Combinatorics, Enumeration
2934	Minimum Operations to Maximize Last Elements in Arrays	Array, Enumeration
2947	Count Beautiful Substrings I	Hash Table, Math, String +3
2975	Maximum Square Area by Removing Fences From a Field	Array, Hash Table, Enumeration
0681	Next Closest TimePremium	Hash Table, String, Backtracking +1
1999	Smallest Greater Multiple Made of Two DigitsPremium	Math, Enumeration
2417	Closest Fair IntegerPremium	Math, Enumeration

Hard (20)

Hard problems
No.	Problem	Topics
0479	Largest Palindrome Product	Math, Enumeration
0829	Consecutive Numbers Sum	Math, Enumeration
0906	Super Palindromes	Math, String, Enumeration
1601	Maximum Number of Achievable Transfer Requests	Bit Manipulation, Array, Backtracking +1
1617	Count Subtrees With Max Distance Between Cities	Bit Manipulation, Tree, Dynamic Programming +2
1761	Minimum Degree of a Connected Trio in a Graph	Graph, Enumeration
2014	Longest Subsequence Repeated k Times	Greedy, String, Backtracking +2
2025	Maximum Number of Ways to Partition an Array	Array, Hash Table, Counting +2
2081	Sum of k-Mirror Numbers	Math, Enumeration
2122	Recover the Original Array	Array, Hash Table, Two Pointers +2
2151	Maximum Good People Based on Statements	Bit Manipulation, Array, Backtracking +1
2234	Maximum Total Beauty of the Gardens	Greedy, Array, Two Pointers +4
2242	Maximum Score of a Node Sequence	Graph, Array, Enumeration +1
2306	Naming a Company	Bit Manipulation, Array, Hash Table +2
2440	Create Components With Same Value	Tree, Depth-First Search, Array +2
2468	Split Message Based on Limit	String, Binary Search, Enumeration
2552	Count Increasing Quadruplets	Binary Indexed Tree, Array, Dynamic Programming +2
2763	Sum of Imbalance Numbers of All Subarrays	Array, Hash Table, Enumeration
2959	Number of Possible Sets of Closing Branches	Bit Manipulation, Graph, Enumeration +2
1956	Minimum Time For K Virus Variants to SpreadPremium	Geometry, Array, Math +2

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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.

Type your message...

GPT-6.1 Terra

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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...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

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...

GPT-6.1 TerraClear chat

Primary display

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Enumeration problems by difficulty

Easy (20)20

Medium (40)40

Hard (20)20

When the Enumeration problem arrives live.

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Easy (20)

Medium (40)

Hard (20)