30 Days DSA Interview Preparation Planby@samirpaul
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30 Days DSA Interview Preparation Plan

by Samir P.October 21st, 2022
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In this repository, I have stored solutions to various problems and concepts of **Data Structures and Algorithms** in Python3 in a structured manner. In various folders of the above topics, you can find questions and concepts related to that topic. In the [SamirPaul1/DSAlgo/main/Main/02_DynamicProgramming] section, all the questions not covered in **Ada Vermama Verma's are included. The repository is hosted by Samir Paul, who uses it to help students understand Python's programming.

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30 Days Interview Preparation Plan🎯

Day1: (Arrays)

  • Sort an array of 0’s 1’s 2’s without using extra space or sorting Algo
  • Repeat and Missing Number
  • Merge two sorted Arrays without extra space
  • Kadane’s Algorithm
  • Merge Overlapping Subintervals
  • Find the duplicate in an array of N+1 integers.

Day2: (Arrays)

  • Set Matrix Zeros
  • Pascal Triangle
  • Next Permutation
  • Inversion of Array (Using Merge Sort)
  • Stock Buy and Sell
  • Rotate Matrix

Day3: (Arrays/maths)

  • Search in a 2D matrix
  • Pow(X,n)
  • Majority Element (>N/2 times)
  • Majority Element (>N/3 times)
  • Grid Unique Paths
  • Reverse Pairs (Leetcode)
  • Go through Puzzles from GFG (Search on your own)

Day4: (Hashing)

  • 2 Sum problem
  • 4 Sum problem
  • Longest Consecutive Sequence
  • Largest Subarray with 0 sum
  • Count the number of subarrays with the given XOR (this clears a lot of problems)
  • Longest substring without repeat

Day5: (LinkedList)

  • Reverse a LinkedList
  • Find the middle of LinkedList
  • Merge two sorted Linked List
  • Remove the N-th node from the back of LinkedList
  • Delete a given Node when a node is given. (0(1) solution)
  • Add two numbers as LinkedList


  • Find the intersection point of Y LinkedList
  • Detect a cycle in Linked List
  • Reverse a LinkedList in groups of size k
  • Check if a LinkedList is a palindrome or not.
  • Find the starting point of the Loop of LinkedList
  • Flattening of a LinkedList
  • Rotate a LinkedList

Day7: (2-pointer)

  • Clone a Linked List with random and next pointer
  • 3 sum
  • Trapping rainwater
  • Remove Duplicate from the Sorted array
  • Max consecutive ones

Day8: (Greedy)

  • N meeting in one room
  • Minimum number of platforms required for a railway
  • Job sequencing Problem
  • Fractional Knapsack Problem
  • Greedy algorithm to find the minimum number of coins
  • Activity Selection (it is the same as N meeting in one room)

Day9 (Recursion):

  • Subset Sums
  • Subset-II
  • Combination sum-
  • Combination sum
  • Palindrome Partitioning
  • K-th permutation Sequence

Day10: (Recursion and Backtracking)

  • Print all Permutations of a string/array
  • N queens Problem
  • SudokuSolver
  • M Coloring Problem
  • Rat in a Maze
  • Word Break -> print all ways

Day11 : (Binary Search)

  • The N-th root of an integer (use binary search) (square root, cube root, ..)
  • Matrix Median
  • Find the element that appears once in the sorted array, and the rest element appears twice (Binary search)
  • Search element in a sorted and rotated array/ find pivot where it is rotated
  • Median of 2 sorted arrays
  • K-th element of two sorted arrays
  • Allocate a Minimum Number of Pages
  • Aggressive Cows

Day12: (Bits) (Optional, very rare topic in interviews, but if you have time left, someone might ask)

  • Check if a number if a power of 2 or not in O(1)
  • Count total set bits
  • Divide Integers without / operator
  • Power Set (this is very important)
  • Find MSB in o(1)
  • Find the square of a number without using multiplication or division operators.

Day13: (Stack and Queue)

  • Implement Stack Using Arrays
  • Implement Queue Using Arrays
  • Implement Stack using Queue (using single queue)
  • Implement Queue using Stack (0(1) amortized method)
  • Check for balanced parentheses
  • Next Greater Element
  • Sort a Stack


  • Next Smaller Element
  • LRU cache (vvvv. imp)
  • LFU Cache (Hard, can be ignored)
  • Largest rectangle in a histogram (Do the one-pass solution)
  • Sliding Window Maximum
  • Implement Min Stack
  • Rotten Orange (Using BFS)
  • Stock Span Problem
  • Find the maximum or minimum of every window size
  • The Celebrity Problem

Day15: (String)

  • Reverse Words in a String
  • Longest Palindrome in a string
  • Roman Number to Integer and vice versa
  • Implement ATOI/STRSTR
  • Longest Common Prefix Rabin Karp

Day16: (String)

  • Prefix Function/Z-Function
  • KMP Algo / LPS(pi) array
  • Minimum characters needed to be inserted in the beginning to make it palindromic.
  • Check for Anagrams Count and Say Compare version numbers

Day17: (Binary Tree)

  • In-order Traversal (with recursion and without recursion)
  • Pre-order Traversal (with recursion and without recursion)
  • Post-order Traversal (with recursion and without recursion)
  • Left View Of Binary Tree
  • Bottom View of Binary Tree
  • Top View of Binary Tree

Day18: (Binary Tree)

  • Level order Traversal / Level order traversal in spiral form
  • Height of a Binary Tree
  • Diameter of Binary Tree
  • Check if the Binary tree is height-balanced or not
  • LCA in Binary Tree
  • Check if the two trees are identical or not

Day 19: (Binary Tree)

  • Maximum path sum
  • Construct Binary Tree from inorder and preorder
  • Construct Binary Tree from Inorder and Postorder
  • Symmetric Binary Tree
  • Flatten Binary Tree to LinkedList
  • Check if Binary Tree is the mirror of itself or not

Day 20: (Binary Search Tree)

  • Populate Next Right pointers of the Tree
  • Search the given Key in BST Construct BST from the given keys.
  • Check if a BT is BST or not
  • Find the LCA of two nodes in BST
  • Find the in-order predecessor/successor of a given Key in BST.

Day21: (BinarySearchTree)

  • Floor and Ceil in a BST
  • Find K-th smallest and K-th largest element in BST (2 different Questions)
  • Find a pair with a given sum in BST
  • BST iterator Size of the largest BST in a Binary Tree
  • Serialize and deserialize Binary Tree

Day22: (Mixed Questions)

  • Binary Tree to Double Linked List
  • Find the median in a stream of running integers.
  • K-th largest element in a stream.
  • Distinct numbers in the Window.
  • K-th largest element in an unsorted array.
  • Flood-fill Algorithm

Day23: (Graph)

  • Clone a graph (Not as easy as it looks)
  • DFS
  • BFS
  • Detect A cycle in Undirected Graph/Directed Graph
  • Topo Sort
  • Number of islands (Do in Grid and Graph both)
  • Bipartite Check

Day24: (Graph)

  • SCC(using KosaRaju’s Algo)
  • Dijkstra's algorithm
  • Bellman-Ford Algo
  • Floyd Warshall Algorithm
  • MST using Prim’s Algo
  • MST using Kruskal’s Algo

Day25: (Dynamic Programming)

  • Max Product Subarray
  • Longest Increasing Subsequence
  • Longest Common Subsequence
  • 0-1 Knapsack
  • Edit Distance
  • Maximum sum increasing subsequence
  • Matrix Chain Multiplication

Day26: (DP)

  • Maximum sum path in the matrix, (count paths and similar types do, also backtrack to find the maximum path)

  • Coin change

  • Subset Sum

  • Rod Cutting

  • Egg Dropping

  • Word Break

  • Palindrome Partitioning (MCM Variation)

  • Maximum profit in Job scheduling

For core revision</>


  • Revise OS notes that you would have made during your sem
  • If not made notes, spend 2 or 3 days and make notes from Knowledge Gate.


  • Revise DBMS notes that you would have made during your semesters.
  • If not made notes, spend 2 or 3 days and make notes from Knowledge Gate.


  • Revise CN notes, that you would have made during your sem.
  • If not made notes, spend 2 or 3 days and make notes from Knowledge Gate.


  • Make a note of how you will represent your projects, and prepare all questions related to tech which you have used in your projects.
  • Prepare a note that you can say for 3-10 minutes when he asks you that say something about the project.

Data Structures & Algorithms for Coding Interview

In this repository, I have stored solutions to various problems and concepts of Data Structures and Algorithms in Python3 in a structured manner.✨

Topics Covered:

  • Dynamic Programming

  • Sorting Algorithms

  • LinkedList

  • Object-Oriented Programming

  • Binary Trees

  • Graph Algorithms

  • Heap

  • Matrix

  • Trie

  • Binary Search

  • Backtracking

  • Stack

  • Queue

  • Greedy

  • String

  • Bit Manipulation

  • Array

  • HashMap


  • Two Pointers

  • Math

  • Recursion

In various folders of the above topics, you can find questions and concepts related to that topic.

  • For learning Dynamic Programming, we need to relate the concepts learned in one question to apply to another problem💡. In the Dynamic Programming section, you can find all the questions covered and not covered in Aditya Verma's dynamic programming playlist folder-wise with my handwritten notes.✍️

  • If you are preparing for an interview from Striver’s SDE Sheet then the 30-Days-SDE-Sheet-Practice will be helpful to you. Here I have stored solutions to questions of each day with short notes to each solution, as short notes about the approach are very helpful during revision.🎯

  • In the Questions-Sheet directory, you can find questions asked by top product-based companies.

  • There is a collection of books and pdfs on various important computer science fundamentals in the BOOKS-and-PDFs directory.📚

View this repository in an online VSCode-like interface▶️ 🚀

I am continuously trying to improve this repository by adding new questions and concepts related to the respective topic. Please feel free to contribute to this repository.💻

If you appreciate my work, please give a star(🌟) to this repository. It motivates me. ❤️🚀