Two Pointers

It is used when we need to find pairs or sub-arrays in an array that satisfy a certain condition, or when we need to find a specific element in a sorted array.

Typically, the two pointers advance towards opposite ends of the data structure with a fixed increment.

Data Usages: Arrays, Linked List, Strings

Sample Problems

Two Sum ➡️ Solution

Two Sum II - Input Array is Sorted

Longest Palindromic Substring

Maximum Sum Subarray

Intersection of Two Linked Lists

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Fast and Slow Pointers

It is used in DSA to solve problems involving linked lists, arrays, or other data structures where we need to iterate the data in a specific way.

The Fast and Slow Pointer technique involves using a "slow" pointer and a "fast" pointer. The slow pointer moves one step at a time, while the fast pointer moves two steps at a time.

Data Usages: Arrays, Strings, Linked Lists

Sample Problems

Linked List Cycle

Middle of a Linked List

Intersection of Two Linked Lists

Remove Nth Node From End of List

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Sliding Window

It is used when we need to find a subarray or a substring that meets certain criteria, such as having a specific sum or product or containing a certain pattern or character and the input data in a specific window size.

Data Usages: Arrays, Strings, Linked Lists

Sample Problems

Maximum Sum Subarray of size k

Longest Substring without repeating characters

Find the Index of the first occurrence in a string

Minimum Window Substring

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In - Place reversal of Linked List

It is used when we need to reverse the order of the elements in the linked list without using any additional data structures such as arrays or other lists.

DSA Usages: Linked List

Sample Problems

Reverse Linked List

Reverse Linked List II

Palindrome Linked List

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Modified Binary Search

This method is used when the conventional binary search algorithm cannot be used to solve the problem because the search condition is more complex than simply checking if an element is greater than or less than the middle element.

Data Usages: Arrays

Sample Problems

Find the Minimum in a Rotated Sorted Array

Find the First and Last Position of the Element in the Sorted Array

Search a 2D Matrix

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Islands (Matrix Traversal)

It is used to solve problems that involve traversing a matrix or grid to find a specific pattern or object. This method is used when the problem requires identifying clusters or groups of cells in the matrix that meet certain criteria.

Data Usages: Matrix, Queue

Sample Problem

Number of Islands

Longest Increasing Path in a Matrix

Count Submatrices with all ones

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Merge Intervals

The Merge Interval is a popular method for solving problems that involve merging or overlapping intervals. It is used when the problem requires combining or merging intervals that share a common overlap or intersection.

Data Usages: Array, Heap

Sample Problems

Merge Intervals

Non-overlapping Intervals

Insert Intervals

Meeting Rooms

Interval List Intersection

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Two Heaps

The Two Heaps is a popular method for solving problems that involve managing and processing elements in two separate heaps simultaneously. It is used when the problem requires maintaining two sets of elements with specific ordering or prioritization properties.

Data Usages: Heap, Array

Sample Problems

Find Median from Data Stream

Kth Smallest Element

Sliding Window Median

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Top 'K' Elements

The Top 'K' Elements is a popular method for solving problems that involve finding or managing the K largest or smallest elements from a collection of elements. It is used when the problem requires identifying the elements with the highest or lowest values based on a specific criterion.

Data Usages: Heap, Arrays

Sample Problems

The least number of Unique integers after k removal

Top K Frequent Elements

K Closest Points to Origin

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K-way Merge

The K-way Merge is a popular method for solving problems that involve merging multiple sorted lists or arrays into a single sorted list or array. It is used when the problem requires combining and sorting elements from multiple sources.

Data Usages: Arrays , Queue, Heap

Sample Problems

Merge K-Sorted Lists

Kth Smallest value in a Sorted Matrix

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Cyclic Sort

The Cyclic Sort is a popular method for solving problems that involve sorting an array of numbers in a specific range. It is used when the problem requires arranging the elements of the array cyclically to achieve the desired order.

Data Usages: Arrays

Sample Problems

Missing Number

Sort Colors

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Breadth-First Search (BFS)

BFS is a popular method for solving problems related to traversing or searching in a graph or tree data structure. It is used when the problem requires exploring or visiting all the vertices or nodes of the graph in a breadth- wise manner, i.e., exploring the vertices at the same level before moving to the next level.

Data Usages: Trees, Graphs, Matrix, Queues

Sample Problems

Shortest Path Visiting All Nodes

Binary Tree Level Order Traversal

Minimum Depth of a Binary Tree

Populate Next Right Pointer in Each Node

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Depth-First Search (DFS)

DFS is a popular method for solving problems related to traversing or searching in a graph or tree data structure. It is used when the problem requires exploring or visiting all the vertices or nodes of the graph in a depth-wise manner, i.e., exploring as far as possible along each branch before backtracking.

Data Usages: Tree Graph Matrix

Sample Problems

Count Number of Complete Components

Find Number of Connected Components in an Undirected Graph

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Topological Sort

The Topological Sort is a popular method for solving problems related to directed acyclic graphs (DAGs). It is used when the problem requires ordering the vertices of a DAG in such a way that for every directed edge (u, v), vertex u comes before vertex v in the ordering.

Data Usages: Arrays hash Table Queues Graphs

Sample Problems

Course Schedule II

Verifying an Alien Dictionary

Path Sum III

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Fibonacci Number

The Fibonacci Numbers method is a mathematical sequence that is frequently used in DSA to solve various problems. It is used when the problem involves calculating or generating the Fibonacci sequence or utilizing the properties of Fibonacci numbers.

Data Usages: Arrays, Hash Table

Sample Problems

Fibonacci Number

Climbing Stairs

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Subsets

The Subsets method is a common algorithmic approach used in DSA to generate or explore all possible subsets of a given set. It is used when the problem involves finding or generating all combinations or subsets of elements from a set.

Data Usages: Queues, Arrays, Strings

Sample Problems

Subsets

Subset Sum Problem

Permutations

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0/1 Knapsack

The 0/1 Knapsack method is a well-known algorithmic approach used in DSA to solve optimization problems, particularly those involving resource allocation or selection. It is used when the problem requires maximizing or minimizing a value while considering constraints on the capacity or availability of resources.

DSA Usages: Array, HashTable

Sample Problems

Target Sum

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Palindromic Subsequence

The Palindromic Subsequence method is a technique used in DSA to solve problems that involve identifying and manipulating palindromic subsequences within a given string or sequence. It is used when the problem requires finding or manipulating palindromic subsequences with specific properties or constraints.

Data Usages: Array, HashTable

Sample Problems

Longest Palindromic Subsequence

Count Different Palindromic Subsequences

Minimum Insertion Steps to make a String Palindrome

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Longest Common Substring

The Longest Common Substring method is used in DSA to solve problems that involve finding the longest common substring between two or more strings. It is used when the problem requires identifying the longest continuous sequence of characters that is common to multiple strings.

DSA Usages: Array, HashTable

Sample Problems

Longest Common Subsequence

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Bitwize XOR

The Bitwise XOR (Exclusive OR) method is used in DSA to solve various problems that involve bitwise operations and manipulation of binary representations of numbers. It is used when the problem requires performing operations or extracting information by manipulating individual bits using XOR logic.

Data Usages: Arrays, Bits

Sample Problems

Single Number