K5kC 150

A curated list of 150 coding problems designed to help you master data structures and algorithms.

Total: 109 problems across 21 categories

string(1)

#	Problem	Difficulty	Video
271	Encode and Decode Strings	medium

hash table(4)

#	Problem	Difficulty
1	Two Sum	easy
217	Contains Duplicate 1 - Check if array has duplicates	easy
242	Valid Anagram	easy
49	Group Anagrams	medium

two pointers(6)

#	Problem	Difficulty	Video
125	Valid Palindrome	easy
844	Backspace String Compare	easy	-
11	Container With Most Water	medium
15	3Sum0 - Find three elements in an array that sum to a zero	medium
75	Dutch National Flag DNF	medium
42	Trapping Rain Water	hard	-

sliding window(6)

#	Problem	Difficulty	Video
3	Longest Substring Without Repeating Characters	medium
424	Longest Substring with Same Letters after Replacement	medium
438	Find anagrams of a string in another string	medium	-
1248	Count Number of Nice Subarrays	medium	-
76	Minimum Window Substring	hard
239	Sliding Window Maximum	hard	-

binary search(5)

#	Problem	Difficulty	Video
704	Binary Search on Sorted Array	easy
33	Search in Rotated Sorted Array	medium
74	Search a 2D Matrix 1 - Elements sorted row-wise and first integer of each row is greater than last element of previous row is greater than last element of previous row	medium	-
153	Find Minimum in Rotated Sorted Array	medium
4	Median of Two Sorted Arrays	hard	-

sorting(3)

#	Problem	Difficulty	Video
179	Largest Number From Given Numbers	medium
215	Kth Largest Element in an Array	medium	-
451	Sort Characters By Frequency	medium	-

bit manipulation(6)

#	Problem	Difficulty
136	Single Number 1 - All elements except one occur twice	easy
190	Reverse Bits	easy
191	Number of 1 Bits	easy
268	Missing Number	easy
338	Counting Bits	easy
371	Sum of Two Integers	medium

math(2)

#	Problem	Difficulty	Video
202	Happy Number	easy	-
149	Maximum Points on a Line	hard	-

linked list(6)

#	Problem	Difficulty	Video
21	Merge Two Sorted Linked Lists	easy
141	Linked List Cycle 1 - Detect Cycle	easy
160	Intersection of Two Linked Lists	easy	-
206	Reverse Linked List	easy
19	Remove Nth Node From End of List	medium
143	Reorder List such that i-th element points to n-i-th element	medium

stack(5)

#	Problem	Difficulty	Video
20	Valid Parentheses	easy
232	Implement Queue using Stacks	easy	-
155	Min Stack	medium	-
739	Daily Temperatures	medium	-
84	Largest Rectangle in Histogram	hard	-

tree(13)

#	Problem	Difficulty	Video
100	Same Tree	easy
101	Symmetric Binary Tree	easy	-
104	Maximum Depth of Binary Tree	easy
226	Invert Binary Tree	easy
572	Subtree of Another Tree	easy
98	Validate Binary Search Tree	medium
102	Binary Tree Level Order Traversal - Level by Level	medium
105	Construct Binary Tree from Inorder and Preorder Traversal	medium
230	Kth Smallest Element in a BST	medium
235	Lowest Common Ancestor of a Binary Search Tree	medium
648	Replace Words	medium	-
124	Binary Tree Path Sum - Maximum between any two nodes	hard
297	Serialize and Deserialize Binary Tree	hard

trie(3)

#	Problem	Difficulty
208	Implement Trie	medium
211	Design Add and Search Words Data Structure	medium
212	Word Search 2 - Return All Words	hard

graph(8)

#	Problem	Difficulty	Video
128	Longest Consecutive Sequence	medium	-
133	Clone Undirected Graph	medium	-
200	Number of Islands	medium
207	Course Schedule 1 - Is it Possible	medium	-
261	Graph Valid Tree	medium	-
417	Pacific Atlantic Water Flow	medium	-
127	Word Ladder 1 - Get Ladder Length	hard	-
269	Alien Dictionary	hard	-

backtracking(5)

#	Problem	Difficulty	Video
39	Combination Sum 1	medium
46	Permutations of Array 1	medium	-
78	Subsets 1	medium
79	Word Search 1 - Find if word exists	medium
51	N-Queens	hard	-

greedy(2)

#	Problem	Difficulty	Video
55	Jump Game 1 - Check if it reaches last index	medium
134	Gas Station	medium	-

interval(5)

#	Problem	Difficulty	Video
252	Meeting Rooms 1 - Can person attend all meetings	easy	-
56	Merge Overlapping Intervals	medium	-
57	Insert Interval	medium	-
253	Maximum Intervals Overlap Count	medium	-
435	Non-overlapping Intervals	medium	-

dynamic programming(15)

#	Problem	Difficulty	Video
70	Climbing Stairs - Take atmost 2 Steps	easy
121	Best Time To Buy And Sell Stock 1 - only one transaction	easy
5	Longest Palindromic Substring	medium
53	Maximum Subarray Sum	medium
62	Unique Paths in Grid 1 - Count all paths moving right or down	medium
91	Decode Ways	medium
139	Word Break 1 - Check if word is breakable	medium
152	Maximum Product Subarray	medium
198	House Robber	medium
213	House Robber 2 - Houses in circle	medium
300	Longest Increasing Subsequence	medium
322	Coin Change with Fewest Number of Coins Given Infinite Supply	medium
416	Partition Equal Subset Sum	medium	-
647	Palindromic Substrings	medium
1143	Longest Common Subsequence LCS 1 - Get Length	medium

union find(4)

#	Problem	Difficulty	Video
323	Number of Connected Components in an Undirected Graph	medium	-
399	Evaluate Division	medium	-
684	Redundant Connection	medium	-
721	Accounts Merge	medium	-

heap priority queue(4)

#	Problem	Difficulty	Video
347	Top K Frequent Elements	medium
621	Task Scheduler	medium	-
23	Merge K Sorted Lists	hard
295	Find Median from Data Stream	hard

matrix(4)

#	Problem	Difficulty	Video
1572	Matrix Diagonal Sum	easy	-
44	Rotate n x n matrix by 90 degrees	medium
54	Spiral Matrix 1 - Return	medium
73	Set Matrix Zeros	medium

prefix sum(1)

#	Problem	Difficulty	Video
238	Product of Array Except Self	medium