75 DAYS CHALLENGE

“The wisest mind has something yet to learn.” ~ George Santayana.

75 days challenge questions sheet

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Array

Day - 1

• 1. Two Sum
• 121. Best Time to Buy and Sell Stock
• 66. Plus One
• 283. Move Zeroes

Day - 2

• 977. Squares of a Sorted Array
• 122. Best Time to Buy and Sell Stock II
• 724. Find Pivot Index
• 169. Majority Element

Day - 3

• 118. Pascals triangle
• 26. Remove duplicates
• 56. Merge intervals
• 15. 3-Sum

Day - 4

• 380. Insert and delete O(1)
• 560. Subarray sum equals k
• 31. Next permutation
• 11. Container With Most Water

Day - 5

• 54. Spiral Matrix
• 48. Rotate Image
• 79. Word Search

Day - 6

• 16. 3Sum Closest
• 289. Game of Life
• 1010. Pairs of Songs With Total Durations Divisible by 60
• 18. 4Sum

Day - 7

• 39. Combination Sum
• 45. Jump Game II
• 1423. Maximum Points You Can Obtain from Cards

Day - 8

• 1465. Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts
• 695. Max Area of Island
• 442. Find All Duplicates in an Array
• 532. K-diff Pairs in an Array

Day - 9

• 1169. Invalid Transactions
• 55. Jump Game
• 974. Subarray Sums Divisible by K

Day - 10

• 123. Best Time to Buy and Sell Stock III
• 41. First Missing Positive
• 84. Largest Rectangle in Histogram

Day - 11

• 381. Insert Delete GetRandom O(1) - Duplicates allowed
• 1499. Max Value of Equation

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Two pointer & Sliding window

Day - 12

• 763. Partition Labels
• 75. Sort Colors

Day - 13

• 424. Longest Repeating Character Replacement
• 992. Subarrays with K Different Integers

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Binary Search

Day - 14

• 1351. Count Negative Numbers in a Sorted Matrix]
• 852. Peak Index in a Mountain Array
• 981. Time Based Key-Value Store
• 33. Search in Rotated Sorted Array

Day - 15

• 50. Pow(x, n)
• 34. Find First and Last Position of Element in Sorted Array
• 162. Find Peak Element
• 74. Search a 2D Matrix

Day - 16

• 29. Divide Two Integers
• 1011. Capacity To Ship Packages Within D Days
• 1760. Minimum Limit of Balls in a Bag
• 4. Median of Two Sorted Arrays

Day - 17

• 315. Count of Smaller Numbers After Self
• 410. Split Array Largest Sum

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Hashing

Day - 18

• Introduction
• Open Addressing
• Collision handling

Day - 19

• 953. Verifying an Alien Dictionary
• 706. Design HashMap
• 347. Top K Frequent Elements

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Linked list

Day - 20

• 206. Reverse Linked List
• 876. Middle of the Linked List
• 21. Merge Two Sorted Lists
• 19. Remove Nth Node From End of List

Day - 21

• 237. Delete Node in a Linked List
• 445. Add Two Numbers II
• 160. Intersection of Two Linked Lists
• 234. Palindrome Linked List

Day - 22

• 25. Reverse Nodes in k-Group
• 142. Linked List Cycle II
• 61. Rotate List

Day - 23

• 430. Flatten a Multilevel Doubly Linked List
• 138. Copy List with Random Pointer
• 287. Find the Duplicate Number

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Stack

Day - 24

• 496. Next Greater Element I
• 503. Next Greater Element II
• 225. Implement Stack using Queues
• 232. Implement Queue using Stacks

Day - 25

• 20. Valid Parentheses
• 155. Min Stack
• Help Classmates
• 146. LRU Cache

Day - 26

• 84. Largest Rectangle in Histogram
• 239. Sliding Window Maximum
• 460. LFU Cache

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Tree

Day - 27

• 543. Diameter of Binary Tree
• 101. Symmetric Tree
• 226. Invert Binary Tree
• 572. Subtree of Another Tree

Day - 28

• 108. Convert Sorted Array to Binary Search Tree
• 617. Merge Two Binary Trees
• 104. Maximum Depth of Binary Tree
• 257. Binary Tree Paths

Day - 29

• 100. Same Tree
• 235. Lowest Common Ancestor of a Binary Search Tree
• 112. Path Sum
• 530. Minimum Absolute Difference in BST

Day - 30

• 404. Sum of Left Leaves
• 110. Balanced Binary Tree
• 662. Maximum Width of Binary Tree
• 1448. Count Good Nodes in Binary Tree

Day - 31

• 236. Lowest Common Ancestor of a Binary Tree
• 199. Binary Tree Right Side View
• 863. All Nodes Distance K in Binary Tree
• 297. Serialize and Deserialize Binary Tree

Day - 32

• 102. Binary Tree Level Order Traversal
• 103. Binary Tree Zigzag Level Order Traversal
• 173. Binary Search Tree Iterator
• 437. Path Sum III

Day - 33

• 116. Populating Next Right Pointers in Each Node
• 114. Flatten Binary Tree to Linked List
• 662. Maximum Width of Binary Tree
• 889. Construct Binary Tree from Preorder and Postorder Traversal

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Binary Search Tree

Day - 34

• [Binary Search Tree

  Set 1 (Search and Insertion)](https://www.geeksforgeeks.org/binary-search-tree-set-1-search-and-insertion/)

• [Binary Search Tree

  Set 2 (Delete)](https://www.geeksforgeeks.org/binary-search-tree-set-2-delete/)

• Floor and Ceil from a BST
• 938. Range Sum of BST

Day - 35

• 108. Convert Sorted Array to Binary Search Tree
• 235. Lowest Common Ancestor of a Binary Search Tree
• 530. Minimum Absolute Difference in BST
• 98. Validate Binary Search Tree

Day - 36

• 95. Unique Binary Search Trees II
• 230. Kth Smallest Element in a BST
• 96. Unique Binary Search Trees
• 99. Recover Binary Search Tree

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Heap

Day - 37

• Binary Heap
• Time Complexity of building a heap
• Applications of Heap Data Structure
• HeapSort
• Why is Binary Heap Preferred over BST for Priority Queue?

Day - 38

• merge k sorted array
• nearly sorted algorithm
• 295. Find Median from Data Stream
• 215. Kth Largest Element in an Array

Day - 39

• 347. Top K Frequent Elements
• 218. The Skyline Problem
• 23. Merge k Sorted Lists

Day - 40

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Greedy

Day - 41

• N meetings in one room
• Activity Selection
• Minimum number of Coins

Day - 42

• Fractional Knapsack
• Minimum Platforms
• Job Sequencing Problem

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Backtracking

Day - 43

• [Rat in a Maze

  Backtracking-2](https://www.geeksforgeeks.org/rat-in-a-maze-backtracking-2/)

• [The Knight’s tour problem

  Backtracking-1](https://www.geeksforgeeks.org/the-knights-tour-problem-backtracking-1/)

• [Subset Sum

  Backtracking-4](https://www.geeksforgeeks.org/subset-sum-backtracking-4/)

Day - 44

• 17. Letter Combinations of a Phone Number