� Coding Interview Problems List
� Array
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Find the missing number in a given integer array of 1 to 100 [Time O(n)]
Find the duplicate number in a given integer array [Space O(n) Time O(n)]
Find the largest and smallest number in an unsorted integer array [Time O(n)]
Find all pairs of an integer array whose sum is equal to a given number [Space
O(n) Time O(n)]
5. Find duplicate numbers in an array containing multiple duplicates [Space O(n)
Time O(n)]
6. Remove duplicates from an array in place
7. Reverse an array in place
8. Find the intersection of two arrays
9. Find the maximum product of two integers in an array
10. Find the minimum value in a rotated sorted array
11. Find the maximum sum subarray (Kadane's algorithm)
12. Rotate an array by k positions
13. Find the subarray with the given sum
14. Merge two sorted arrays
15. Move all zeros to the end of an array
16. Find the majority element in an array (Boyer-Moore voting algorithm)
17. Find the equilibrium index of an array
18. Rearrange an array such that even index elements are smaller and odd index elements
are greater
19. Find the largest subarray with equal number of 0s and 1s
20. Find the smallest subarray with a sum greater than a given value
� Strings
21. Reverse a string in place
22. Check if two strings are anagrams of each other
23. Find all permutations of a string
24. Find the first non-repeating character in a string
25. Count the occurrence of a given character in a string
26. Remove duplicate characters from a string
27. Check if a string is a palindrome
28. Convert a given string into an integer
29. Find the longest substring without repeating characters
30. Find the longest common prefix
31. Convert a given string into its integer equivalent (atoi)
32. Check if a string is a valid shuffle of two distinct strings
33. Implement strstr() to find the first occurrence of a substring
34. Find the longest repeating subsequence in a string
35. Remove all adjacent duplicates in a string
36. Check if one string is a rotation of another
37. Find the smallest window in a string containing all characters of another string
38. Find the longest palindromic substring
39. Convert a string to title case (capitalize first letter of each word)
40. Count and say the sequence for a given number
� Linked List
41. Reverse a linked list
42. Detect a cycle in a linked list
43. Find the middle element of a linked list
44. Remove the nth node from the end of a linked list
45. Merge two sorted linked lists
46. Remove duplicates from a linked list
47. Find the intersection point of two linked lists
48. Detect and remove a loop in a linked list
49. Add two numbers represented by linked lists
50. Check if a linked list is a palindrome
51. Implement a singly linked list
52. Implement a doubly linked list
53. Delete a node in a singly linked list given only access to that node
54. Find the intersection point of two linked lists using two pointers
55. Split a linked list into two equal halves
56. Sort a linked list using merge sort
57. Flatten a multilevel linked list
58. Remove nodes that have a greater value on the right
59. Clone a linked list with next and random pointer
60. Implement a skip list
� Stack and Queue
61. Implement a stack using an array/linked list
62. Implement a queue using an array/linked list
63. Implement a stack using two queues
64. Implement a queue using two stacks
65. Sort a stack
66. Evaluate a postfix expression using a stack
67. Implement a priority queue
68. Check for balanced parentheses in an expression
69. Find the maximum element in a stack in O(1) time
70. Implement a circular queue
71. Design a stack that supports getMin() in O(1) time
72. Implement efficient k stacks in a single array
73. Implement an LFU cache
74. Generate binary numbers from 1 to n using a queue
75. Reverse the first k elements of a queue
76. Check if all the leaves are at the same level in a binary tree using a queue
77. Implement a monotonic queue
78. Check for redundancy in an arithmetic expression
79. Design a stack that supports push, pop, top, and retrieving the maximum in O(1)
80. Implement a deque using a doubly linked list
� Tree
81. Traverse a binary tree (preorder, inorder, postorder)
82. Implement a binary search tree (BST)
83. Find the height of a binary tree
84. Find the lowest common ancestor (LCA) of two nodes
85. Check if a binary tree is balanced
86. Check if two binary trees are identical
87. Find the maximum depth of a binary tree
88. Find the diameter of a binary tree
89. Convert a binary tree to a doubly linked list
90. Print all nodes at distance k from a given node
91. Convert a BST to a balanced BST
92. Print the nodes of a binary tree in vertical order
93. Find the level of a node in a binary tree
94. Connect nodes at the same level
95. Construct a binary tree from preorder and inorder traversal
96. Construct a binary tree from inorder and postorder traversal
97. Serialize and deserialize a binary tree
98. Find the inorder successor in a BST
99. Check if a binary tree is a subtree of another
100.
Find the sum of all left leaves in a binary tree
� Graph
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Implement DFS and BFS
Find the shortest path in an unweighted graph
Detect a cycle in a directed/undirected graph
Find strongly connected components
Implement Dijkstra's algorithm
Implement Prim's algorithm
Implement Kruskal's algorithm
Find the shortest path in a weighted graph
Check if a graph is bipartite
Find the number of islands in a 2D matrix
Implement Floyd-Warshall algorithm
Detect a negative cycle in a graph
Find articulation points in a graph
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Find bridges in a graph
� Sorting and Searching
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Implement quicksort
Implement mergesort
Implement heapsort
Implement binary search
Find the kth largest element in an unsorted array
Search for a number in a rotated sorted array
Count occurrences of a number in a sorted array
Search for a range in a sorted array
Sort an array with many duplicates
Find the median of two sorted arrays
Find the kth smallest element in a BST
Sort an array using heapsort
Sort a nearly sorted (K-sorted) array
Find the fixed point in a given array
Perform exponential search
Implement interpolation search
Search in a row-wise and column-wise sorted matrix
Count inversions in an array
Find the peak element in an array
Find the frequency of an element in a sorted array
� Dynamic Programming
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Implement Fibonacci sequence (DP)
Solve the Knapsack problem
Longest Common Subsequence
Longest Increasing Subsequence
Edit Distance problem
Coin Change problem
Maximum Subarray problem
Egg Dropping problem
0/1 Knapsack problem
Minimum Path Sum problem
Rod Cutting problem
Longest Bitonic Subsequence
Matrix Chain Multiplication
Subset Sum problem
Count subsets with a given sum
Target Sum problem
Minimum Insertions to form a Palindrome
Maximum Product Subarray
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Maximum Length of Pair Chain
Word Break problem
� Hashing
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Implement a hash table
Design a hash map
Check if two strings are anagrams using a hash table
Find the first non-repeating character using a hash map
Find the longest substring with distinct characters using a hash map
Count frequency of elements in an array using a hash map
Group anagrams using a hash table
Check for pair sum in an array using hashing
Find the largest subarray with 0 sum
Find the longest consecutive subsequence
� Advanced Topics
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Implement a Trie (Prefix Tree)
Find the shortest path in a maze
Solve the N-Queens problem
Implement a Red-Black Tree
Implement an AVL Tree
Find the maximum flow in a flow network (Ford-Fulkerson)
Implement Rabin-Karp algorithm (substring search)
Implement KMP algorithm (pattern matching)
Solve the Traveling Salesman Problem (DP)
Solve the Graph Coloring problem
� System Design
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Design a URL shortening service
Design a cache system
Design a messaging queue
Design a file storage system (Dropbox/Google Drive)
Design a search autocomplete system
Design a rate limiter
Design a parking lot system
Design a ride-sharing service (Uber/Lyft)
Design a social media feed system
Design a hotel reservation system
� Algorithm Analysis & Complexity
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Analyze time and space complexity of an algorithm
Determine Big-O notation
Compare time complexity of algorithms
Optimize an algorithm for better performance
Identify bottlenecks in an algorithm
Prove correctness of an algorithm
Find amortized time complexity of a data structure operation
Analyze performance of recursive algorithms
Use DP to optimize a recursive solution
Solve problems using divide and conquer
� Miscellaneous
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Design a vending machine
Design an elevator system
Design a library management system
Design a hospital management system
Design a movie ticket booking system
Design an online food ordering system
Design a document editor (Google Docs)
Design a photo-sharing application (Instagram)
Design a web crawler
Design an email service (Gmail)
Implement an LRU cache
Implement an MRU cache
Implement a random access data structure
Design a logging system
Implement a thread-safe bounded blocking queue
Design a file compression system
Design a voting system
Design a fraud detection system
Design a recommendation system
Design a blockchain
� Coding Challenges (LeetCode style)
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Two Sum
Add Two Numbers
Longest Substring Without Repeating Characters
Median of Two Sorted Arrays
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Longest Palindromic Substring
Container With Most Water
Trapping Rain Water
Multiply Strings
Permutations
Rotate Image
Group Anagrams
Maximum Subarray
Spiral Matrix
Jump Game
Merge Intervals
Insert Interval
Subsets
Word Search
Binary Tree Inorder Traversal
Validate Binary Search Tree
Symmetric Tree
Binary Tree Level Order Traversal
Convert Sorted Array to BST
Minimum Depth of Binary Tree
Path Sum
Construct Binary Tree from Preorder & Inorder Traversal
Binary Tree Maximum Path Sum
Longest Consecutive Sequence
Single Number
Linked List Cycle
Reorder List
Maximum Product Subarray
Find Minimum in Rotated Sorted Array
Search in Rotated Sorted Array
Find Peak Element
Word Ladder
Clone Graph
Course Schedule
Implement Trie (Prefix Tree)
Word Search II
Maximal Rectangle
Palindrome Partitioning
Surrounded Regions
Number of Islands
Best Time to Buy and Sell Stock
Best Time to Buy and Sell Stock II
Best Time to Buy and Sell Stock III
Single Number II
Maximum Gap
Factorial Trailing Zeroes
Majority Element
Excel Sheet Column Number
Rotate Array
Binary Tree Right Side View
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Largest Number
Basic Calculator
Range Sum Query - Immutable
Contains Duplicate
Summary Ranges
House Robber
Implement Stack using Queues
Implement Queue using Stacks
Number of Digit One
Count Primes
Find the Duplicate Number
Ugly Number
Missing Number
Product of Array Except Self
Sliding Window Maximum
Kth Largest Element in an Array
Coin Change
Combination Sum
Permutation Sequence
Remove Nth Node From End of List
Longest Increasing Subsequence
Reconstruct Itinerary