Question bank

DSA interview questions

474 data structures and algorithms questions from the Practick bank. Each has the problem, test cases, the clarifying questions worth asking and the follow-ups interviewers use. Read one, then practise it out loud with a real engineer: that is where most rounds are won or lost.

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Data structures (179)

Introduction to Singly LinkedList Easy
Insertion at the head of Linked List Easy
Deletion of the head of LL Easy
Find the length of the Linked List Easy
Introduction to Doubly LL Easy
Insert node before head in Doubly Linked List Easy
Delete head of Doubly Linked List Easy
Middle of a LinkedList [TortoiseHare Method] Easy
Implement Stack using Arrays Easy
Implement Queue using Arrays Easy
Implement Stack using Queue Easy
Implement Queue using Stack Easy
Implement stack using Linkedlist Easy
Implement queue using Linkedlist Easy
Balanced Paranthesis Easy
Postfix to Infix Conversion Easy
Number of Greater Elements to the Right Easy
Heaps (Theory Video) Easy
Sort K sorted array Easy
Replace Elements by Their Rank Easy
Introduction to Trees Easy
Binary Tree Representation in Java Easy
Pre, Post, Inorder in one traversal Easy
Preorder Traversal Easy
Inorder Traversal of Binary Tree Easy
Postorder Traversal Easy
Level Order Traversal Easy
Iterative Preorder Traversal of Binary Tree Easy
Iterative Inorder Traversal of Binary Tree Easy
Post-order Traversal of Binary Tree using 2 stack Easy
Post-order Traversal of Binary Tree using 1 stack Easy
Preorder, Inorder, and Postorder Traversal in one Traversal Easy
Diameter of Binary Tree Easy
Count total nodes in a complete BT Easy
Introduction to Graph Easy
Graph Representation | C++ Easy
Graph Representation | Java Easy
MST theory Easy
Bit PreRequisites for TRIE Problems Easy
Remove Outermost Parentheses Medium
Maximum Nesting Depth of the Parentheses Medium
Search in Linked List Medium
Reverse a Doubly Linked List Medium
Reverse a LinkedList [Iterative] Medium
Reverse a LL Medium
Detect a loop in LL Medium
Find the starting point in LL Medium
Length of loop in LL Medium
Check if LL is palindrome or not Medium
Segregate odd and even nodes in Linked List Medium
Remove Nth node from the back of the LL Medium
Delete the middle node in LL Medium
Sort a Linked List of 0's 1's and 2's Medium
Find the intersection point of Y LL Medium
Add one to a number represented by LL Medium
Add two numbers in Linked List Medium
Find Pairs with Given Sum in Doubly Linked List Medium
Sort a stack using recursion Medium
Reverse a Stack Medium
Infix to Postfix Conversion Medium
Prefix to Infix Conversion Medium
Prefix to Postfix Conversion Medium
Postfix to Prefix Conversion Medium
Infix to Prefix Conversion Medium
Next Greater Element Medium
Next Greater Element - 2 Medium
Next Smaller Element Medium
Asteroid Collision Medium
Sum of Subarray Ranges Medium
Remove K Digits Medium
LRU Cache Medium
Implement Min Heap Medium
Check if an array represents a min heap Medium
Convert Min Heap to Max Heap Medium
K-th Largest element in an array Medium
Kth smallest element in an array [use priority queue] Medium
Task Scheduler Medium
Hand of Straights Medium
Design Twitter Medium
Minimum Cost to Connect Sticks Medium
Top K Frequent Elements Medium
Maximum Depth in BT Medium
Check for balanced binary tree Medium
Check if two trees are identical or not Medium
Zig Zag or Spiral Traversal Medium
Boundary Traversal Medium
Vertical Order Traversal Medium
Top View of BT Medium
Bottom view of BT Medium
Right/Left View of Binary Tree Medium
Symmetric Binary Tree Medium
Print root to leaf path in BT Medium
Maximum Width of BT Medium
Children Sum Property in Binary Tree Medium
Requirements needed to construct a unique BT Medium
Flatten Binary Tree to Linked List Medium
Construct a BST from a preorder traversal Medium
Connected Components Medium
Traversal Techniques Medium
DFS Medium
Number of provinces Medium
Connected Components Problem in Matrix Medium
Rotten Oranges Medium
Flood fill algorithm Medium
Distance of nearest cell having one Medium
Surrounded Regions Medium
Number of enclaves Medium
Number of islands Medium
Course Schedule II Medium
Network Delay Time Medium
Most stones removed with same row or column Medium
Swim in Rising Water Medium
Longest Word with All Prefixes Medium
Number of distinct substrings in a string Medium
Minimize Max Distance to Gas Station Hard
Sort LL Hard
Delete all occurrences of a key in DLL Hard
Remove duplicates from sorted DLL Hard
Reverse LL in group of given size K Hard
Rotate a LL Hard
Flattening of LL Hard
Clone a LL with random and next pointer Hard
M Coloring Problem Hard
Implement Min Stack Hard
Trapping Rainwater Hard
Largest rectangle in a histogram Hard
Stock span problem Hard
Celebrity Problem Hard
LFU Cache Hard
Merge K sorted Lists Hard
Kth largest element in a stream of running integers Hard
Maximum Sum Combination Hard
Find Median from Data Stream Hard
Valid Paranthesis Checker Hard
LCA in BT Hard
Print all nodes at a distance of K in BT Hard
Minimum time taken to burn the BT from a given Node Hard
Construct a BT from Preorder and Inorder Hard
Construct the Binary Tree from Postorder and Inorder Traversal Hard
Serialize and De-serialize BT Hard
Morris Preorder Traversal of a Binary Tree Hard
Morris Inorder Traversal of a Binary Tree Hard
Merge 2 BST's Hard
Cycle Detection in Undirected Graph (bfs) Hard
Detect a cycle in an undirected graph Hard
Word ladder I Hard
Word ladder II Hard
Bipartite Graph (DFS) Hard
Cycle Detection in Directed Graph (DFS) Hard
Topo Sort Hard
Topological sort or Kahn's algorithm Hard
Detect a cycle in a directed graph Hard
Course Schedule I Hard
Find eventual safe states Hard
Alien Dictionary Hard
Shortest path in undirected graph with unit weights Hard
Shortest path in DAG Hard
Djisktra's Algorithm Hard
Why priority Queue is used in Djisktra's Algorithm Hard
Shortest Distance in a Binary Maze Hard
Path with minimum effort Hard
Minimum multiplications to reach end Hard
Bellman Ford Algorithm Hard
Find the city with the smallest number of neighbors Hard
Prim's Algorithm Hard
Disjoint Set Hard
Find the MST weight Hard
Number of operations to make network connected Hard
Accounts merge Hard
Number of islands II Hard
Making a large island Hard
Bridges in graph Hard
Articulation point in graph Hard
Kosaraju's algorithm Hard
Trie Implementation and Operations Hard
Trie Implementation and Advanced Operations Hard
Maximum XOR of two numbers in an array Hard
Maximum Xor with an element from an array Hard
Minimum number of bracket reversals to make an expression balanced Hard

Algorithms (295)

Input Output Easy
Cpp Basics Easy
If ElseIf Easy
Switch Case Easy
What are arrays, strings? Easy
For loops Easy
While loops Easy
Functions (Pass by Reference and Value) Easy
Theory with examples Easy
Easy and Medium Easy
Hard Easy
Pattern 1 Easy
Pattern 2 Easy
Pattern 3 Easy
Pattern 4 Easy
Pattern 5 Easy
Pattern 6 Easy
Pattern 7 Easy
Pattern 8 Easy
Pattern 9 Easy
Pattern 10 Easy
Pattern 11 Easy
Pattern 12 Easy
Pattern 13 Easy
Pattern 14 Easy
Pattern 15 Easy
Pattern 16 Easy
Pattern 17 Easy
Pattern 18 Easy
Pattern 19 Easy
STL Easy
Java Collections Easy
Count all Digits of a Number Easy
Reverse a number Easy
Palindrome Number Easy
GCD of Two Numbers Easy
Check if the Number is Armstrong Easy
Print all Divisors Easy
Check for Prime Number Easy
Understand recursion by print something N times Easy
Print name N times using recursion Easy
Print 1 to N using Recursion Easy
Print N to 1 using Recursion Easy
Sum of First N Numbers Easy
Factorial of a given number Easy
Reverse an array Easy
Check if String is Palindrome or Not Easy
Fibonacci Number Easy
Basic Hashing Easy
Counting Frequencies of Array Elements Easy
Highest Occurring Element in an Array Easy
Selection Sort Easy
Bubble Sort Easy
Insertion Sorting Easy
Recursive Bubble Sort Easy
Recursive Insertion Sort Easy
Largest Element Easy
Second Largest Element Easy
Check if the Array is Sorted II Easy
Remove duplicates from Sorted array Easy
Left Rotate Array by One Easy
Left Rotate Array by K Places Easy
Move Zeros to End Easy
Linear Search Easy
Union of two sorted arrays Easy
Find missing number Easy
Maximum Consecutive Ones Easy
Two Sum Easy
Majority Element-I Easy
Stock Buy and Sell Easy
Leaders in an Array Easy
Pascal's Triangle I Easy
Search X in sorted array Easy
Lower Bound Easy
Upper Bound Easy
Search insert position Easy
Floor and Ceil in Sorted Array Easy
Count Occurrences in a Sorted Array Easy
Find out how many times the array is rotated Easy
Kth Missing Positive Number Easy
Find row with maximum 1's Easy
Largest Odd Number in a String Easy
Longest Common Prefix Easy
Isomorphic String Easy
Rotate String Easy
Check if two strings are anagram of each other Easy
Sort Characters by Frequency Easy
Count Number of Substrings Easy
Pow(x, n) Easy
Learn All Patterns of Subsequences (Theory) Easy
Count all subsequences with sum K Easy
Check if there exists a subsequence with sum K Easy
Introduction to Bits and Tricks Easy
Check if the i-th bit is Set or Not Easy
Check if a Number is Odd or Not Easy
Check if a Number is Power of 2 or Not Easy
Count the Number of Set Bits Easy
Set/Unset the rightmost unset bit Easy
Swap Two Numbers Easy
Divisors of a Number Easy
Pow(x,n) Easy
Assign Cookies Easy
Lemonade Change Easy
Jump Game - I Easy
Introduction to BST Easy
Search in a Binary Search Tree Easy
Find Min/Max in BST Easy
Floor and Ceil in a BST Easy
Floor in a Binary Search Tree Easy
Introduction to DP Easy
Assign Cookies Easy
Count Square Submatrices with All Ones Easy
Hashing In Strings | Theory Easy
Pattern 20 Medium
Pattern 21 Medium
Pattern 22 Medium
Merge Sorting Medium
Quick Sorting Medium
Find the number that appears once, and other numbers twice Medium
Longest subarray with given sum K (positives) Medium
Longest subarray with sum K Medium
Sort an array of 0's 1's and 2's Medium
Kadane's Algorithm Medium
Print subarray with maximum subarray sum Medium
Rearrange array elements by sign Medium
Next Permutation Medium
Longest Consecutive Sequence in an Array Medium
Set Matrix Zeroes Medium
Rotate matrix by 90 degrees Medium
Print the matrix in spiral manner Medium
Count subarrays with given sum Medium
3 Sum Medium
4 Sum Medium
Largest Subarray with Sum 0 Medium
Merge Overlapping Subintervals Medium
Merge two sorted arrays without extra space Medium
Find the repeating and missing number Medium
Count Inversions Medium
Maximum Product Subarray in an Array Medium
First and last occurrence Medium
Search in rotated sorted array-I Medium
Search in rotated sorted array-II Medium
Find minimum in Rotated Sorted Array Medium
Single element in a Sorted Array Medium
Find peak element Medium
Find square root of a number Medium
Find Nth root of a number Medium
Koko eating bananas Medium
Minimum days to make M bouquets Medium
Find the smallest divisor Medium
Capacity to Ship Packages Within D Days Medium
Painter's Partition Medium
Kth element of 2 sorted arrays Medium
Search in a 2D matrix Medium
Search in 2D matrix - II Medium
Find Peak Element - II Medium
Matrix Median Medium
Reverse words in a given string / Palindrome Check Medium
Roman to Integer Medium
String to Integer (atoi) Medium
Longest Palindromic Substring Medium
Sum of Beauty of All Substrings Medium
Reverse every word in a string Medium
Recursive Implementation of atoi() Medium
Count Good Numbers Medium
Generate Binary Strings Without Consecutive 1s Medium
Generate Parentheses Medium
Power Set Medium
Combination Sum Medium
Combination Sum II Medium
Subsets I Medium
Subsets II Medium
Combination Sum III Medium
Word Break Medium
Divide two numbers without multiplication and division Medium
Minimum Bit Flips to Convert Number Medium
Single Number - I Medium
Power Set Bit Manipulation Medium
XOR of numbers in a given range Medium
Single Number - III Medium
Sum of Subarray Minimums Medium
Longest Substring Without Repeating Characters Medium
Max Consecutive Ones III Medium
Fruit Into Baskets Medium
Maximum Points You Can Obtain from Cards Medium
Subarrays with K Different Integers Medium
Fractional Knapsack Medium
N meetings in one room Medium
Jump Game II Medium
Minimum number of platforms required for a railway Medium
Job sequencing Problem Medium
Shortest Job First Medium
Program for Least Recently Used (LRU) Page Replacement Algorithm Medium
Insert Interval Medium
Merge Intervals Medium
Non-overlapping Intervals Medium
Maximum path sum Medium
Insert a given node in BST Medium
Delete a node in BST Medium
Kth Smallest and Largest element in BST Medium
Check if a tree is a BST or not Medium
LCA in BST Medium
Inorder Successor/Predecessor in BST Medium
Climbing stairs Medium
Frog Jump Medium
Frog jump with K distances Medium
Maximum sum of non adjacent elements Medium
House robber Medium
Ninja's training Medium
Grid Unique Paths Medium
Unique paths II Medium
Minimum Falling Path Sum Medium
Triangle Medium
Ninja and his Friends Medium
Best time to buy and sell stock Medium
Best time to buy and sell stock II Medium
Best time to buy and sell stock III Medium
Best time to buy and sell stock IV Medium
Best Time to Buy and Sell Stock with Cooldown Medium
Best time to buy and sell stock with transaction fees Medium
Longest Increasing Subsequence Medium
Print Longest Increasing Subsequence Medium
Longest Increasing Subsequence (DP-43) Medium
Largest Divisible Subset Medium
Longest String Chain Medium
Longest Bitonic Subsequence Medium
Number of Longest Increasing Subsequences Medium
Different Ways to Evaluate a Boolean Expression Medium
Partition Array for Maximum Sum Medium
Majority Element-II Hard
Count subarrays with given xor K Hard
Reverse Pairs Hard
Aggressive Cows Hard
Book Allocation Problem Hard
Split array - largest sum Hard
Median of 2 sorted arrays Hard
Letter Combinations of a Phone Number Hard
Palindrome partitioning Hard
Word Search Hard
N Queen Hard
Rat in a Maze Hard
Sudoku Solver Hard
Expression Add Operators Hard
Print Prime Factors of a Number Hard
Count primes in range L to R Hard
Prime factorisation of a Number Hard
Maximum Rectangles Hard
Sliding Window Maximum Hard
Longest Repeating Character Replacement Hard
Binary Subarrays With Sum Hard
Count number of Nice subarrays Hard
Number of Substrings Containing All Three Characters Hard
Longest Substring With At Most K Distinct Characters Hard
Minimum Window Substring Hard
Minimum Window Subsequence Hard
Candy Hard
Two Sum In BST | Check if there exists a pair with Sum K Hard
Correct BST with two nodes swapped Hard
Largest BST in Binary Tree Hard
Cheapest flight within K stops Hard
Number of ways to arrive at destination Hard
Floyd warshall algorithm Hard
Subset sum equal to target Hard
Partition equal subset sum Hard
Partition a set into two subsets with minimum absolute sum difference Hard
Count subsets with sum K Hard
Count partitions with given difference Hard
Minimum Coins Hard
Target sum Hard
Coin Change 2 Hard
Unbounded knapsack Hard
Rod Cutting Problem Hard
Longest common subsequence Hard
Print Longest Common Subsequence Hard
Longest common substring Hard
Longest palindromic subsequence Hard
Minimum insertions to make string palindrome Hard
Minimum insertions or deletions to convert string A to B Hard
Shortest common supersequence Hard
Distinct subsequences Hard
Edit distance Hard
Wildcard matching Hard
Matrix chain multiplication Hard
Matrix Chain Multiplication | Bottom-Up Hard
Minimum cost to cut the stick Hard
Burst balloons Hard
Palindrome partitioning II Hard
Maximum Rectangle Area with all 1's Hard
Count and say Hard
Rabin Karp Algorithm Hard
Z function Hard
KMP Algorithm or LPS array Hard
Shortest Palindrome Hard
Longest happy prefix Hard
Minimum characters to make string palindrome Hard

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