Easy LeetCode Problems: All 760, With Python Solutions

Easy problems test whether you can turn a stated requirement into working code without fumbling the mechanics. The technique is usually named in the problem; the work is the edge cases.

The rating is LeetCode's own, carried through unchanged — we do not re-score anything. This library holds 760 Easy-rated problems, 588 of them with a complete Python solution, a worked example and complexity analysis.

The patterns behind easy problems

The six patterns with the most Easy-rated problems in this library. Working through a pattern beats working down a difficulty list, because the technique transfers and a difficulty band does not.

Hash Map · 227 Easy problems — Trade memory for time: remember what you have seen so the second pass never happens.
Math and Number Theory · 121 Easy problems — Find the closed form, the invariant, or the modular identity — and skip the loop entirely.
Sorting · 80 Easy problems — Spend O(n log n) once to buy an ordering that makes the rest of the problem trivial.
Two Pointers · 58 Easy problems — Use the order already in the input to discard half the search space at every step.
Depth-First Search · 41 Easy problems — Follow one path to its end before trying the next — the default way to explore a graph.
Greedy · 41 Easy problems — Take the locally best option every time — when you can prove that never costs you later.

Easy problems

Showing the first 200 of 760 problems. Problems with a complete Python solution are listed first, then by ascending problem number.

#	Problem	Difficulty	Topics
1	Two Sum	Easy	Array, Hash Table
9	Palindrome Number	Easy	Math
13	Roman to Integer	Easy	Hash Table, Math, String
14	Longest Common Prefix	Easy	Trie, Array, String
20	Valid Parentheses	Easy	Stack, String
21	Merge Two Sorted Lists	Easy	Recursion, Linked List
26	Remove Duplicates from Sorted Array	Easy	Array, Two Pointers
27	Remove Element	Easy	Array, Two Pointers
28	Find the Index of the First Occurrence in a String	Easy	Two Pointers, String, String Matching
35	Search Insert Position	Easy	Array, Binary Search
58	Length of Last Word	Easy	String
66	Plus One	Easy	Array, Math
67	Add Binary	Easy	Bit Manipulation, Math, String +1
69	Sqrt(x)	Easy	Math, Binary Search
70	Climbing Stairs	Easy	Memoization, Math, Dynamic Programming
83	Remove Duplicates from Sorted List	Easy	Linked List
88	Merge Sorted Array	Easy	Array, Two Pointers, Sorting
94	Binary Tree Inorder Traversal	Easy	Stack, Tree, Depth-First Search +1
100	Same Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
101	Symmetric Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
104	Maximum Depth of Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
108	Convert Sorted Array to Binary Search Tree	Easy	Tree, Binary Search Tree, Array +2
110	Balanced Binary Tree	Easy	Tree, Depth-First Search, Binary Tree
111	Minimum Depth of Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
112	Path Sum	Easy	Tree, Depth-First Search, Breadth-First Search +1
118	Pascal's Triangle	Easy	Array, Dynamic Programming
119	Pascal's Triangle II	Easy	Array, Dynamic Programming
121	Best Time to Buy and Sell Stock	Easy	Array, Dynamic Programming
125	Valid Palindrome	Easy	Two Pointers, String
136	Single Number	Easy	Bit Manipulation, Array
141	Linked List Cycle	Easy	Hash Table, Linked List, Two Pointers
144	Binary Tree Preorder Traversal	Easy	Stack, Tree, Depth-First Search +1
145	Binary Tree Postorder Traversal	Easy	Stack, Tree, Depth-First Search +1
160	Intersection of Two Linked Lists	Easy	Hash Table, Linked List, Two Pointers
168	Excel Sheet Column Title	Easy	Math, String
169	Majority Element	Easy	Array, Hash Table, Divide and Conquer +2
171	Excel Sheet Column Number	Easy	Math, String
175	Combine Two Tables	Easy	Database
181	Employees Earning More Than Their Managers	Easy	Database
182	Duplicate Emails	Easy	Database
183	Customers Who Never Order	Easy	Database
190	Reverse Bits	Easy	Bit Manipulation, Divide and Conquer
191	Number of 1 Bits	Easy	Bit Manipulation, Divide and Conquer
193	Valid Phone Numbers	Easy	Shell
195	Tenth Line	Easy	Shell
196	Delete Duplicate Emails	Easy	Database
197	Rising Temperature	Easy	Database
202	Happy Number	Easy	Hash Table, Math, Two Pointers
203	Remove Linked List Elements	Easy	Recursion, Linked List
205	Isomorphic Strings	Easy	Hash Table, String
206	Reverse Linked List	Easy	Recursion, Linked List
217	Contains Duplicate	Easy	Array, Hash Table, Sorting
219	Contains Duplicate II	Easy	Array, Hash Table, Sliding Window
222	Count Complete Tree Nodes	Easy	Bit Manipulation, Tree, Binary Search +1
225	Implement Stack using Queues	Easy	Stack, Design, Queue
226	Invert Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
228	Summary Ranges	Easy	Array
231	Power of Two	Easy	Bit Manipulation, Recursion, Math
232	Implement Queue using Stacks	Easy	Stack, Design, Queue
234	Palindrome Linked List	Easy	Stack, Recursion, Linked List +1
242	Valid Anagram	Easy	Hash Table, String, Sorting
257	Binary Tree Paths	Easy	Tree, Depth-First Search, String +2
258	Add Digits	Easy	Math, Number Theory, Simulation
263	Ugly Number	Easy	Math
268	Missing Number	Easy	Bit Manipulation, Array, Hash Table +3
278	First Bad Version	Easy	Binary Search, Interactive
283	Move Zeroes	Easy	Array, Two Pointers
290	Word Pattern	Easy	Hash Table, String
292	Nim Game	Easy	Brainteaser, Math, Game Theory
303	Range Sum Query - Immutable	Easy	Design, Array, Prefix Sum
326	Power of Three	Easy	Recursion, Math
338	Counting Bits	Easy	Bit Manipulation, Dynamic Programming
342	Power of Four	Easy	Bit Manipulation, Recursion, Math
344	Reverse String	Easy	Two Pointers, String
345	Reverse Vowels of a String	Easy	Two Pointers, String
349	Intersection of Two Arrays	Easy	Array, Hash Table, Two Pointers +2
350	Intersection of Two Arrays II	Easy	Array, Hash Table, Two Pointers +2
367	Valid Perfect Square	Easy	Math, Binary Search
374	Guess Number Higher or Lower	Easy	Binary Search, Interactive
383	Ransom Note	Easy	Hash Table, String, Counting
387	First Unique Character in a String	Easy	Queue, Hash Table, String +1
389	Find the Difference	Easy	Bit Manipulation, Hash Table, String +1
392	Is Subsequence	Easy	Two Pointers, String, Dynamic Programming
401	Binary Watch	Easy	Bit Manipulation, Backtracking
404	Sum of Left Leaves	Easy	Tree, Depth-First Search, Breadth-First Search +1
405	Convert a Number to Hexadecimal	Easy	Bit Manipulation, Math, String
409	Longest Palindrome	Easy	Greedy, Hash Table, String
412	Fizz Buzz	Easy	Math, String, Simulation
414	Third Maximum Number	Easy	Array, Sorting
415	Add Strings	Easy	Math, String, Simulation
434	Number of Segments in a String	Easy	String
441	Arranging Coins	Easy	Math, Binary Search
448	Find All Numbers Disappeared in an Array	Easy	Array, Hash Table
455	Assign Cookies	Easy	Greedy, Array, Two Pointers +1
459	Repeated Substring Pattern	Easy	String, String Matching
461	Hamming Distance	Easy	Bit Manipulation
463	Island Perimeter	Easy	Depth-First Search, Breadth-First Search, Array +1
476	Number Complement	Easy	Bit Manipulation
482	License Key Formatting	Easy	String
485	Max Consecutive Ones	Easy	Array
492	Construct the Rectangle	Easy	Math
495	Teemo Attacking	Easy	Array, Simulation
496	Next Greater Element I	Easy	Stack, Array, Hash Table +1
500	Keyboard Row	Easy	Array, Hash Table, String
501	Find Mode in Binary Search Tree	Easy	Tree, Depth-First Search, Binary Search Tree +1
504	Base 7	Easy	Math, String
506	Relative Ranks	Easy	Array, Sorting, Heap (Priority Queue)
507	Perfect Number	Easy	Math
509	Fibonacci Number	Easy	Recursion, Memoization, Math +1
511	Game Play Analysis I	Easy	Database
520	Detect Capital	Easy	String
521	Longest Uncommon Subsequence I	Easy	String
530	Minimum Absolute Difference in BST	Easy	Tree, Depth-First Search, Breadth-First Search +2
541	Reverse String II	Easy	Two Pointers, String
543	Diameter of Binary Tree	Easy	Tree, Depth-First Search, Binary Tree
551	Student Attendance Record I	Easy	String
557	Reverse Words in a String III	Easy	Two Pointers, String
559	Maximum Depth of N-ary Tree	Easy	Tree, Depth-First Search, Breadth-First Search
561	Array Partition	Easy	Greedy, Array, Counting Sort +1
563	Binary Tree Tilt	Easy	Tree, Depth-First Search, Binary Tree
566	Reshape the Matrix	Easy	Array, Matrix, Simulation
572	Subtree of Another Tree	Easy	Tree, Depth-First Search, Binary Tree +2
575	Distribute Candies	Easy	Array, Hash Table
577	Employee Bonus	Easy	Database
584	Find Customer Referee	Easy	Database
586	Customer Placing the Largest Number of Orders	Easy	Database
589	N-ary Tree Preorder Traversal	Easy	Stack, Tree, Depth-First Search
590	N-ary Tree Postorder Traversal	Easy	Stack, Tree, Depth-First Search
594	Longest Harmonious Subsequence	Easy	Array, Hash Table, Counting +2
595	Big Countries	Easy	Database
596	Classes With at Least 5 Students	Easy	Database
598	Range Addition II	Easy	Array, Math
599	Minimum Index Sum of Two Lists	Easy	Array, Hash Table, String
605	Can Place Flowers	Easy	Greedy, Array
607	Sales Person	Easy	Database
610	Triangle Judgement	Easy	Database
617	Merge Two Binary Trees	Easy	Tree, Depth-First Search, Breadth-First Search +1
619	Biggest Single Number	Easy	Database
620	Not Boring Movies	Easy	Database
627	Swap Sex of Employees	Easy	Database
628	Maximum Product of Three Numbers	Easy	Array, Math, Sorting
637	Average of Levels in Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
643	Maximum Average Subarray I	Easy	Array, Sliding Window
645	Set Mismatch	Easy	Bit Manipulation, Array, Hash Table +1
653	Two Sum IV - Input is a BST	Easy	Tree, Depth-First Search, Breadth-First Search +4
657	Robot Return to Origin	Easy	String, Simulation
661	Image Smoother	Easy	Array, Matrix
671	Second Minimum Node In a Binary Tree	Easy	Tree, Depth-First Search, Binary Tree
674	Longest Continuous Increasing Subsequence	Easy	Array
680	Valid Palindrome II	Easy	Greedy, Two Pointers, String
682	Baseball Game	Easy	Stack, Array, Simulation
693	Binary Number with Alternating Bits	Easy	Bit Manipulation
696	Count Binary Substrings	Easy	Two Pointers, String
697	Degree of an Array	Easy	Array, Hash Table
700	Search in a Binary Search Tree	Easy	Tree, Binary Search Tree, Binary Tree
703	Kth Largest Element in a Stream	Easy	Tree, Design, Binary Search Tree +3
704	Binary Search	Easy	Array, Binary Search
705	Design HashSet	Easy	Design, Array, Hash Table +2
706	Design HashMap	Easy	Design, Array, Hash Table +2
709	To Lower Case	Easy	String
717	1-bit and 2-bit Characters	Easy	Array
724	Find Pivot Index	Easy	Array, Prefix Sum
728	Self Dividing Numbers	Easy	Math
733	Flood Fill	Easy	Depth-First Search, Breadth-First Search, Array +1
744	Find Smallest Letter Greater Than Target	Easy	Array, Binary Search
746	Min Cost Climbing Stairs	Easy	Array, Dynamic Programming
747	Largest Number At Least Twice of Others	Easy	Array, Sorting
748	Shortest Completing Word	Easy	Array, Hash Table, String
762	Prime Number of Set Bits in Binary Representation	Easy	Bit Manipulation, Math
766	Toeplitz Matrix	Easy	Array, Matrix
771	Jewels and Stones	Easy	Hash Table, String
783	Minimum Distance Between BST Nodes	Easy	Tree, Depth-First Search, Breadth-First Search +2
796	Rotate String	Easy	String, String Matching
804	Unique Morse Code Words	Easy	Array, Hash Table, String
806	Number of Lines To Write String	Easy	Array, String
812	Largest Triangle Area	Easy	Geometry, Array, Math
819	Most Common Word	Easy	Array, Hash Table, String +1
821	Shortest Distance to a Character	Easy	Array, Two Pointers, String
824	Goat Latin	Easy	String
830	Positions of Large Groups	Easy	String
832	Flipping an Image	Easy	Bit Manipulation, Array, Two Pointers +2
836	Rectangle Overlap	Easy	Geometry, Math
844	Backspace String Compare	Easy	Stack, Two Pointers, String +1
859	Buddy Strings	Easy	Hash Table, String
860	Lemonade Change	Easy	Greedy, Array
867	Transpose Matrix	Easy	Array, Matrix, Simulation
868	Binary Gap	Easy	Bit Manipulation
872	Leaf-Similar Trees	Easy	Tree, Depth-First Search, Binary Tree
876	Middle of the Linked List	Easy	Linked List, Two Pointers
883	Projection Area of 3D Shapes	Easy	Geometry, Array, Math +1
884	Uncommon Words from Two Sentences	Easy	Hash Table, String, Counting
888	Fair Candy Swap	Easy	Array, Hash Table, Binary Search +1
892	Surface Area of 3D Shapes	Easy	Geometry, Array, Math +1
896	Monotonic Array	Easy	Array
897	Increasing Order Search Tree	Easy	Stack, Tree, Depth-First Search +2
905	Sort Array By Parity	Easy	Array, Two Pointers, Sorting
908	Smallest Range I	Easy	Array, Math
914	X of a Kind in a Deck of Cards	Easy	Array, Hash Table, Math +2
917	Reverse Only Letters	Easy	Two Pointers, String
922	Sort Array By Parity II	Easy	Array, Two Pointers, Sorting

Keep exploring

Medium problems1,579 problemsEvery Medium-rated LeetCode problem in the library, with Python solutions.Hard problems661 problemsEvery Hard-rated LeetCode problem in the library, with Python solutions.LeetCode patternsAll the techniques, each with a Python template and its complexity.Blind 7575 problemsThe Blind 75: a 75-problem list assembled from the patterns that keep reappearing in technical interviews, grouped by topic. Every entry links to a Python solution with complexity analysis.

Everything at once: the full LeetCode problem list.

A easy problem, live, with someone watching

Stealth Interview is a desktop app for macOS and Windows. It reads the coding problem off your screen, returns a working solution with a step-by-step explanation and its time and space complexity, and transcribes what the interviewer is saying — while staying invisible to screen sharing.

Get Stealth Interview See pricing