KennethWang1221/Leetcode

Leetcode Practice

Problem Lists

This repo records coding problems from leetcode. All problems are organized by the corresponding category

Basic Data Structures

Arrays

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0011	Container With Most Water	Array / Two Pointers		1 2	✔️	Top Interview 0029/150
0026	Remove Duplicates from Sorted Array	Array / Two Pointers		1 2	✔️	Top Interview 0003/150
0031	Next Permutation	Array		1 2	✔️
0042	Trapping Rain Water	Array / Two Pointers / DP		1 2	✔️	Top Interview 0016/150
0048	Rotate Image	Array / Matrix		1 2	✔️	Top Interview 0037/150
0054	Spiral Matrix	Array / Matrix		1 2 3	✔️	Top Interview 0036/150
0056	Merge Intervals	Array / Intervals		1 2	✔️	Top Interview 0050/150
0057	Insert Interval	Array / Intervals / Similar to Leetcode_0056_Merge_Intervals		1 2	✔️	Top Interview 0051/150
0452	Minimum Number of Arrows to Burst Balloons	Array / Intervals / Similar to Leetcode_0056_Merge_Intervals		1 2	✔️	Top Interview 0052/150
0228	Summary Ranges	Array / Intervals		1	✔️	Top Interview 0049/150
0075	Sort Colors	Array		1 2	✔️
0088	Merge Sorted Array	Bubble_sort / Sorting / Two Pointers		1 2	✔️	Recap Bubble Sort / Top Interview 0001/150
0189	Rotate Array	Array / Two Pointers		1 2	✔️	Top Interview 0006/150
0283	Move Zeroes	Array		1	✔️
0496	Next Greater Element I	Array		1	✔️
0503	Next Greater Element II	Array		1	✔️
0941	Valid Mountain Array	Array		1 2	✔️
1260	Shift 2D Grid	Array		1	✔️
sort	sort algorithm	10 sort algoritmes		1	✔️
0027	Remove Element	Two Pointers		1	✔️	Top Interview 0002/150
0080	Remove Duplicates Sorted Array II	Array / Two Pointers		1	✔️	Top Interview 0004/150
0238	Product of Array Except Self	Array / Prefix sum		1	✔️	Top Interview 0013/150
0209	Minimum Size Subarray Sum	Array / Sliding Window		1	✔️	Top Interview 0031/150
0036	Valid Sudoku	Array / Matrix		1	✔️	Top Interview 0035/150
0073	Set Matrix Zeroes	Array / Matrix		1	Need Investigate	Top Interview 0038/150
0289	Game of List	Array / Matrix		1	Need Investigate	Top Interview 0039/150
0053	Maximum Subarray	Kadane's Algorithm		1	✔️	Top Interview 0111/150
0918	Maximum Sum Circular Subarray	Kadane's Algorithm		1	✔️	Top Interview 0112/150

String

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0006	Zigzag Conversion	String		1 2	✔️	Top Interview 0022/150
0008	String to Integer (atoi)	String		1	✔️
0014	Longest Common Prefix	String		1	✔️	Top Interview 0023/150
0028	Implement strStr	String		1	✔️	Top Interview 0024/150
0151	Reverse Words in a String	String		1 2	✔️	Top Interview 0020/150
0186	Reverse Words in a String II	Stack / Two Pointers		1 2	✔️
0344	Reverse String	String		1	✔️
0415	Add Strings	String		1	✔️
0443	String Compression	String		1	✔️
0459	Repeated Substring Pattern	KMP		1	✔️
0541	Reverse String II	String		1 2 3	✔️
0551	Student Attendance Record I	String		1	✔️	bool recap
0557	Reverse Words in a String III	String		1	✔️
0809	Expressive Words	String		1	✔️
0824	Goat Latin	String		1	✔️
0848	Shifting Letters	String		1	✔️
0937	Reorder Data in Log Files	String		1	✔️
1047	Remove All Adjacent Duplicates In String	String		1	✔️
0058	Length of Last Word	String		1	✔️	Top Interview 0019/150
0068	Text Justification	String		1	Need Investigate	Top Interview 0025/150
0125	Valid Palindrome	String / Two Pointers		1	✔️	Top Interview 0026/150
0392	Is Subsequence	String / Two Pointers		1	✔️	Top Interview 0027/150

Linked List

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0002	Add Two Numbers	Linked List		1 2	✔️	Top Interview 0059/150
0019	Remove Nth Node From End of List	fast/slow pointer		1	✔️	Top Interview 0062/150
0021	Merge Two Sorted Lists	Linked List		1	✔️	Top Interview 0060/150
0023	Merge k Sorted Lists	Divide&Conquer / Recursive / Binary Search		1 2 3 4 5	✔️	Top Interview 0111/150
0024	Swap Nodes in Pairs	Linked List		1 2 3 4	✔️
0025	Reverse Nodes in k-Group	Linked List		1	✔️	Top Interview 0066/150
0061	Rotate List	fast/slow pointers		1 2	✔️	Top Interview 0064/150
0082	Remove Duplicates from Sorted List II	Linked List		1	✔️	Top Interview 0063/150
0083	Remove Duplicates from Sorted List	Linked List		1 2	✔️
0086	Partition List	Linked List / similar to Leetcode 21. Merge Two Sorted Lists and Leetcode_0328_odd_even_linkedlist.ipynb		1 2	✔️	Top Interview 0067/150
0092	Reverse Linked List II	Linked List		1	✔️	Top Interview 0061/150
0141	Linked List Cycle	Linked List		1 2	✔️	Top Interview 0058/150
0142	Linked List Cycle II	Linked List		1	✔️
0147	Insertion Sort List	Linked List		1	✔️
0148	Sort List	Divide & Conquer		1 2 3	✔️	Top Interview 0109/150
0160	Intersection of Two Linked Lists	Linked List		1	✔️
0203	Remove Linked List Elements	Linked List		1	✔️
0206	Reverse Linked List	Linked List		1	✔️
0237	Delete Node in a Linked List	Linked List		1	✔️
0328	Odd Even Linked List	Linked List		1	✔️
0445	Add Two Numbers II	Linked List		1	✔️
0707	Design Linked List	Linked List		1	✔️
0725	Split Linked List in Parts	Linked List		1	✔️
0876	Middle of the Linked List	Linked List		1	✔️
0138	Copy List with Random Pointer	Linked List		1	✔️	Top Interview 0065/150

Queue

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0225	Implement Stack using Queues	Queue		1	✔️

Stack

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0150	Evaluate Reverse Polish Notation	Stack		1	✔️	Top Interview 0056/150
0155	Min Stack	Stack		1	✔️	Top Interview 0055/150
0232	Implement Queue using Stacks	Stack		1 2 3 4 5	✔️
0316	Remove Duplicate Letters	Stack		1	✔️
0739	Daily Temperatures	Stack		1	✔️
0946	Validate Stack Sequences	Stack		1	✔️
1249	Minimum Remove to Make Valid Parentheses	Stack		1	✔️
0020	Valid Parentheses	Stack		1 2	✔️	Top Interview 0053/150
0071	Simplify Path	Stack		1	✔️	Top Interview 0054/150
0224	Basic Calculator	Stack		1	✔️	Top Interview 0057/150

Advanced Data Structures

HashSet / HashTable

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0001	Two Sum	HashMap		1 2 3	✔️	Top Interview 0045/150
0003	Longest Substring Without Repeating Characters	HashMap / Sliding Window		1	✔️	Top Interview 0032/150
0015	3Sum	HashMap / Two Pointers		1	✔️	Top Interview 0030/150
0018	4Sum	HashMap		1	✔️
0128	Longest Consecutive Sequence	HashMap		1	✔️	Top Interview 0048/150
0167	Two Sum II - Input Array Is Sorted	HashMap / Two Pointers		1 2	✔️	Top Interview 0028/150
0202	Happy Number	HashMap		1	✔️	Top Interview 0046/150
0205	Isomorphic Strings	HashMap / Zip		1	✔️	Top Interview 0041/150
0217	Contains Duplicate	HashMap		1	✔️
0242	Valid Anagram	HashMap		1 2	✔️	Top Interview 0043/150 / same solution to Leetcode_0383_Ransom_Note
0347	Top K Frequent Elements	HashMap		1	✔️
0349	Intersection of Two Arrays	HashMap / Array		1	✔️
0383	Ransom Note	HashMap / Array		1	✔️	Top Interview 0040/150
0387	First Unique Character in a String	HashMap		1	✔️
0442	Find All Duplicates in an Array	HashMap		1	✔️
0454	4Sum II	HashMap		1	✔️
0560	Subarray Sum Equals K	HashMap		1	✔️
0594	Longest Harmonious Subsequence	HashMap		1 2	✔️
0705	Design HashSet	HashMap		1	✔️
0953	Verifying an Alien Dictionary	HashMap		1	✔️
1002	Find Common Characters	HashMap		1	✔️
0169	Majority Element	Array / HashMap / Divide and Conquer		1	✔️	Top Interview 0005/150
0380	Insert Delete GetRandom O(1)	Array / HashMap / Math		1	✔️	Top Interview 0012/150
0013	Roman To Integer	Array / HashMap / Math / String		1	✔️	Top Interview 0017/150
0012	Integer To Roman	Array / HashMap / Math / String		1	✔️	Top Interview 0018/150
0076	Minimum Window Substring	HashMap / Sliding Window		1	✔️	Top Interview 0033/150
0030	Substring with Concatenation of All Words	HashMap / Sliding Window		1	Need Investigate	Top Interview 0034/150
0290	Word Pattern	HashMap		1	✔️	Top Interview 0042/150
0049	Group Anagrams	HashMap		1 2	✔️ Top Interview 0044/150
0219	Contains Duplicate II	HashMap / Sliding Window / Add HashMap DIY method, similar to Leetcode_0217_Contains_Duplicate		1	✔️	Top Interview 0047/150

Tree

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0094	Binary Tree Inorder Traversal	Recursive		1 2	✔️
0098	Validate Binary Search Tree	Recursive		1 2	✔️	Top Interview 0087/150
0230	Kth Smallest Element in a BST	BFS / BST		1 2	✔️	Top Interview 0088/150
0100	Same Tree	Recursive		1	✔️	Top Interview 0069/150
0101	Symmetric Tree	Recursion / Iterative using stack or que / BFS		1	✔️	Top Interview 0071/150
0102	Binary Tree Level Order Traversal	Recursion / Iterative using list or que / BFS		1 2 3	✔️	Top Interview 0084/150
0103	Binary Tree Zigzag Level Order Traversal	BFS		1	✔️	Top Interview 0085/150
0104	Maximum Depth of Binary Tree	BFS / DFS / same as Leetcode_0102		1	✔️	Top Interview 0068/150
0105	Construct Binary Tree from Preorder and Inorder Traversal	Recursive		1	✔️	Top Interview 0072/150
0106	Construct Binary Tree from Inorder and Postorder Traversal	Recursive		1	✔️	Top Interview 0073/150
0107	Binary Tree Level Order Traversal II	BFS / DFS		1	✔️
0199	Binary Tree Right Side View	BFS / DFS		1	✔️	Top Interview 0082/150
0637	Average of Levels in Binary Tree	BFS / DFS		1	✔️	Top Interview 0083/150
0429	N-ary Tree Level Order Traversal	BFS / DFS		1	✔️
0515	Find Largest Value in Each Tree Row	BFS / DFS		1	✔️
0116	Populating Next Right Pointers in Each Node	BFS / DFS		1 2	✔️
0117	Populating Next Right Pointers in Each Node II	BFS / DFS		1	✔️	Top Interview 0074/150
0111	Minimum Depth of Binary Tree	BFS / DFS		1	✔️
0114	Flatten Binary Tree to Linked List	DFS		1	✔️	Top Interview 0075/150
0108	Convert Sorted Array to Binary Search Tree	Recursive / Divide & conquer		1 2	✔️	Top Interview 0108/150
0110	Balanced Binary Tree	Recursive		1 2	✔️
0112	Path Sum	Recursive / Preorder traversal DFS		1 2	✔️	Top Interview 0076/150
0113	Path Sum II	Recursive / Iterative		1	✔️
0129	Sum Root to Leaf Numbers	Preorder Traversal DFS / Recursive / Same as Leetcode_0112_Path_Sum		1 2	✔️	Top Interview 0077/150
0124	Binary Tree Maximum Path Sum	Recursive / Iterative		1 2	Need Investigate	Top Interview 0081/150
0144	Binary Tree Preorder Traversal	Recursion / Iterative		1	✔️
0145	Binary Tree Postorder Traversal	Recursion / Iterative		1	✔️
0199	Binary Tree Right Side View	BFS		1	✔️
0222	Count Complete Tree Nodes	BFS / Recursive		1	✔️	Top Interview 0078/150
0226	Invert Binary Tree	DFS-Recursive / DFS-Iterative / BFS		1	✔️	Top Interview 0070/150
0235	Lowest Common Ancestor of a Binary Search Tree	DFS-Recursive / DFS-Iterative / BFS		1	✔️
0236	Lowest Common Ancestor of a Binary Tree	Recursive		1	✔️	Top Interview 0079/150
0173	Binary Search Tree Iterator	Binary Search Tree		1	Need Investigate	Top Interview 0080/150
0257	Binary Tree Paths	Recursive / Iterative		1	✔️
0404	Sum of Left Leaves	Recursive / Iterative		1	✔️
0429	N-ary Tree Level Order Traversal	Recursive / Iterative		1	✔️
0450	Delete Node in a BST	Recursive		1	✔️
0501	Find Mode in Binary Search Tree	DFS-Iterative		1	✔️
0513	Find Bottom Left Tree Value	BFS		1	✔️
0530	Minimum Absolute Difference in BST	BFS / DFS		1	✔️	Top Interview 0086/150
0538	Convert BST to Greater Tree	BFS / DFS		1 2	✔️
0572	Subtree of Another Tree	Recursion		1	✔️
0617	Merge Two Binary Trees	Recursion		1	✔️
0637	Average of Levels in Binary Tree	BFS		1	✔️
0654	Maximum Binary Tree	Recursion		1 2	✔️
0669	Trim a Binary Search Tree	Recursion		1 2	✔️
0700	Search in a Binary Search Tree	Recursion / Iterative		1	✔️
0701	Insert into a Binary Search Tree	Recursion / Iterative		1	✔️

Heap

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0295	Find Median from Data Stream	Heap		1 2	✔️	Recap Heap can see Leetcode_1584
0973	K Closest Points to Origin	Heap		1	✔️	Recap Heap
0703	Kth Largest Element in a Stream	Heap		1	✔️
0215	Kth Largest Element in an Array	Heap / Quick Select		1	✔️
0692	Top K Frequent Words	Heap / Dict		1 2	Need Investigate

Graph (Breadth-FS)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0127	Word Ladder	HashMap		1	✔️
0200	Number of Islands	BFS / DFS		1 2	✔️	Top Interview 0089/150
0207	Course Schedule	BFS / Iterative		1	✔️	Top Interview 0093/150
0210	Course Schedule II	BFS / Iterative		1	✔️	Top Interview 0094/150
0310	Minimum Height Trees	Topological		1 2 3
0463	Island Perimeter	DFS		1	✔️
1466	Reorder Routes to Make All Paths Lead to the City Zero	BFS		1	✔️
0286	Walls and Gates	Multi-Source BFS		1	✔️
0787	Cheapest Flights Within K Stops	Ballman-Ford Algorithm		1	✔️
0994	Rotting Oranges	BFS		1	✔️
0752	Open the Lock	BFS		1		Need Investigate
0934	Shortest Bridge	BFS / DFS		1		Need Investigate
0909	Snakes and Ladders	BFS		1	✔️	Top Interview 0095/150
0433	Minimum Genetic Mutation	BFS / DFS / same idea as Leetcode_0127		1	✔️	Top Interview 0096/150
0127	Word Ladder	BFS		1	✔️	Top Interview 0097/150

Graph (Best-FS)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Graph (DFS)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0133	Clone Graph	DFS		1 2	Need Investiage	Top Interview 0091/150
0399	Evaluate Division	DFS		1	✔️	Top Interview 0092/150
0417	Pacific Atlantic Water Flow	DFS		1	✔️
0743	Network Delay Time	Djikstra		1 2	✔️
0261	Graph Valid Tree	DFS		1	✔️
0212	Word Search II	DFS / Trie / Backtracking		1		Top Interview 0099/150
1584	Min Cost to Connect All Points	Minimum Cost Spanning Tree / Prim's Algorithm		1	✔️	Recap heapq & Learn Prim's Algorithm
1905	Count Sub Islands	DFS		1	✔️	Similar as Leetcode_0200_Number_of_Islands
0778	Swim in Rising Water	Dijkstra's Algorithm		1	✔️
0130	Surrounded Regions	Reverse thinking / Graph DFS		1	✔️	Top Interview 0090/150
0695	Max Area of Island	DFS		1	✔️	Similar to Leetcode_0200_Number_of_Islands.ipynb
0332	Reconstruct Itinerary	DFS		1	✔️
0329	Longest Increasing Path in a Matrix	DFS		1	✔️
0802	Find Eventual Safe States	DFS		1		Need Investigate

Basic Algorithms

Binary Search

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Breadth-First Search

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Best-First Search

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Depth-First Search

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Backtracking

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0079	Word Search	DFS		1	✔️	Top Interview 0107/150
0017	Letter Combinations of a Phone Number	DFS		1	✔️	Top Interview 0101/150
0077	Combinations	DFS		1	✔️	Top Interview 0102/150
0046	Permutations	DFS		1	✔️	Top Interview 0103/150
0039	Combination Sum	DFS		1	✔️	Top Interview 0104/150
0052	N-Queens II	DFS		1	✔️	Top Interview 0105/150
0022	Generate Parentheses	DFS		1	✔️	Top Interview 0106/150

Divide & Conquer

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0148	Sort List	Divide & Conquer		1 2 3	✔️	Top Interview 0109/150
0108	Convert Sorted Array to Binary Search Tree	Recursive / Divide & conquer / Binary Search		1 2	✔️	Top Interview 0108/150
0427	Construct Quad Tree	Recursive / Divide & conquer / Binary Search		1	✔️	Top Interview 0110/150

Dynamic Programming 1D

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0121	Best Time to Buy and Sell Stock	Array / DP / Sliding Window		1	✔️	Top Interview 0007/150 / Understand for-loop and while-loop
0122	Best Time to Buy and Sell Stock II	Array / DP / Sliding Window / Greedy		1	✔️	Top Interview 0008/150 / Understand DP
0055	Jump Game	Array / DP / Greedy		1	✔️	Top Interview 0009/150 / Understand DP & Greedy
0055	Jump Game II	Array / DP / Greedy		1	✔️	Top Interview 0010/150 / Understand DP & Greedy
0274	H-Index	Array / Soring / binary_Search		1	✔️	Top Interview 0011/150
0134	Gas_Station	Greedy		1	✔️	Top Interview 0014/150
0135	Candy	Greedy / Two Passes of Linear scans		1	✔️	Top Interview 0015/150

Dynamic Programming 1D (Multiple States)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Dynamic Programming 2D (2D Input)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Dynamic Programming 2D (Two 1D Inputs)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0072	Edit Distance	DP		1 2	✔️	Bottom-up DP

Dynamic Programming 2D (1D Input)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Dynamic Programming 2D (1D Input + K)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Dynamic Programming (Knapsack)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Dynamic Programming (Others)

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Math

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Advanced Algorithms

Trie

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0208	Implement Trie Prefix Tree	Trie / Prefix Tree		1	✔️	Top Interview 0098/150
0211	Design Add and Search Words Data Structure	Trie / Prefix Tree		1	✔️	Top Interview 0100/150

Union Find

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0684	Redundant Connection	Graph Problems - Union Find		1		Need Investigate
0323	Number of Connected Components in an Undirected Graph	Graph Problems - Union Find		1		Need Investigate

Topological Sort

Number	Problem	Solution	Difficulty	Reference	Accepted	Note
0269	Alien Dictionary - Topological Sort	Graph Problems - Graph		1		Need Investigate

Boyer-Moore Voting Algorithm

Number	Problem	Solution	Difficulty	Reference	Accepted	Note

Complex Problems

HashTable + Doubly Linked List

Number	Problem	Solution	Difficulty	Reference	Accepted	Note