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Dashboard DSA Guide Java DSA Business Guide

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DSA Guide
Java DSA
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Java DSA.

A structured path through Java — fundamentals, DSA foundations, the main data structures & algorithms, and core Java / OOP. Check items off as you go; progress is saved in this browser.

4 Modules655 Topics0 Solved

Print Hello World
Add two numbers from input
Simple calculator

Print name, age, GPA with printf formatting
Read a full line then an int (nextLine pitfall)
Convert seconds to HH:MM:SS

Fast input with BufferedReader for 10^5 numbers
Parse a mixed-token line without Scanner
Format a table of N rows with aligned columns

Swap two numbers
Area of circle
Percentage of marks

Swap without a third variable
Detect int overflow and fix with long
Celsius ↔ Fahrenheit with casting

Add two huge numbers using long and carry
Multiply two ints safely (Math.multiplyExact)
Explain and print char arithmetic results

Even or odd
Largest of two numbers
Last digit of a number

Count digits of a number
Check power of 2 using operators
Sum of digits

Evaluate tricky ++/-- expressions
Swap using XOR
Reverse digits without loops

Leap year
Grade from marks
Largest of three

Calculator with switch
Triangle type from three sides
Day of week from number

Date validity check (with leap years)
Quadratic roots classification
Number to words (up to 999)

Print 1 to N
Multiplication table
Sum of first N numbers

Check prime
Reverse a numberLeetCode
Fibonacci series up to N

Print all primes up to N efficiently
Count trailing zeros of N!
Collatz sequence length for max in range

Pattern 1: Square starN x N block of stars
Pattern 2: Right-angled star triangle1, 2, 3 ... N stars per row
Pattern 3: Right-angled number triangle1 / 1 2 / 1 2 3 ...
Pattern 4: Same-number triangle1 / 2 2 / 3 3 3 ...
Pattern 5: Inverted star triangleN stars shrinking down to 1
Pattern 6: Inverted number triangle1 2 3 4 5 / 1 2 3 4 / ... / 1
Pattern 7: Star pyramidCentered pyramid of stars with leading spaces

Pattern 8: Inverted star pyramidUpside-down centered pyramid
Pattern 9: Diamond starPyramid joined with an inverted pyramid
Pattern 10: Half diamond starStars grow to N, then shrink back
Pattern 11: Binary number triangle1 / 0 1 / 1 0 1 / 0 1 0 1 ...
Pattern 12: Number crown1 . . . 1 / 1 2 . 2 1 / 1 2 3 2 1 with a gap in the middle
Pattern 13: Increasing number triangle1 / 2 3 / 4 5 6 / 7 8 9 10 ...
Pattern 14: Increasing letter triangleA / A B / A B C ...
Pattern 15: Reverse letter triangleA B C D E / A B C D / ... / A
Pattern 16: Alpha-rampA / B B / C C C ...
Pattern 17: Alpha-hillLetter pyramid: A / A B A / A B C B A ...

Pattern 18: Alpha-triangleE / D E / C D E ... (letters counted from the end)
Pattern 19: Symmetric-voidStars on both sides with a growing empty gap
Pattern 20: Symmetric-butterflyButterfly shape made of stars
Pattern 21: Hollow rectangleStars only on the border
Pattern 22: The number patternConcentric squares of numbers (3 3 3 / 3 2 3 / 3 3 3)

Factorial method
Is prime method
Max of two (overloaded for int/double)

nCr using methods
Power function x^n
Armstrong check method

Fast exponentiation with mod
Method to return min and max (array or object)
Recursion-free GCD of an array

Sum of Array Elements
Count of odd numbers in Array
Check if the Array is Sorted I
Reverse an array
Linear Search
Largest Element
Second Largest Element

Maximum Consecutive OnesLeetCode
Left Rotate Array by One
Left Rotate Array by K PlacesLeetCode
Move Zeros to EndLeetCode
Remove duplicates from sorted arrayLeetCode
Find missing numberLeetCode
Union of two sorted arrays
Intersection of two sorted arraysLeetCode

Print the matrix in spiral mannerLeetCode
Rotate matrix by 90 degreesLeetCode
Set Matrix ZeroesLeetCode

Reverse a String IILeetCode
Palindrome Check
Largest Odd Number in a StringLeetCode
Longest Common PrefixLeetCode

Isomorphic StringsLeetCode
Rotate StringLeetCode
Valid AnagramLeetCode
Sort Characters by FrequencyLeetCode

String to Integer (atoi)LeetCode
Longest Palindromic SubstringLeetCode
Sum of Beauty of All SubstringsLeetCode

Linear Search
Search X in sorted arrayLeetCode
Lower Bound

Upper Bound
Search insert positionLeetCode
First and last occurrenceLeetCode
Count Occurrences in a Sorted Array

Floor and Ceil in Sorted Array
Search in rotated sorted array-ILeetCode

Selection Sort
Bubble Sort
Insertion Sorting

Recursive Bubble Sort
Recursive Insertion Sort

Count all Digits of a Number
Count number of odd digits in a number
Reverse a numberLeetCode
Palindrome NumberLeetCode
Return the Largest Digit in a Number
Factorial of a given number
Check if the Number is Armstrong
Check for Perfect NumberLeetCode

Check for Prime Number
Count of Prime Numbers till NLeetCode
GCD of Two Numbers
LCM of two numbers
Divisors of a Number

Print all primes till N
Prime factorisation of a Number
Count primes in range L to R

Sum of First N Numbers
Factorial of a Given Number
Sum of Array Elements II
Reverse a String ILeetCode
Check if String is Palindrome or Not
Check if a Number is Prime or Not
Reverse an array 2
Check if the Array is Sorted II
Sum of Digits in a Given Number

Fibonacci NumberLeetCode
Pow(x,n)LeetCode
Power SetLeetCode

Generate Binary Strings Without Consecutive 1s
Check if there exists a subsequence with sum K
Count all subsequences with sum K

Highest Occurring Element in an Array

Second Highest Occurring Element
Sum of Highest and Lowest Frequency
Longest Consecutive Sequence in an ArrayLeetCode

Longest subarray with sum K
Count subarrays with given sumLeetCode
Count subarrays with given xor K

Merge Sorting
Quick Sorting

Sort an array of 0's 1's and 2'sLeetCode
Merge IntervalsLeetCode

Count Inversions
Reverse PairsLeetCode

Find complexity of a single loop
Find complexity of nested loops
Space complexity of recursion factorial

Complexity of loop with i *= 2
Complexity of recursive Fibonacci
Compare two solutions of two-sum

Analyse complexity of merge sort recurrence
Amortised analysis of dynamic array append
Estimate if O(n²) fits for n = 10^6

Reverse an ArrayList
Remove duplicates using HashSet
Count word frequency with HashMap

Sort a list of objects with Comparator
Top K frequent elements
Valid parentheses with Stack

LRU Cache using LinkedHashMap
Sliding window maximum with Deque
Merge K sorted lists with PriorityQueue

Linear Search
Largest Element
Second Largest Element
Maximum Consecutive OnesLeetCode
Left Rotate Array by One
Left Rotate Array by K PlacesLeetCode
Move Zeros to EndLeetCode
Remove duplicates from sorted arrayLeetCode
Find missing numberLeetCode
Union of two sorted arrays
Intersection of two sorted arraysLeetCode

Majority Element-ILeetCode
Leaders in an Array
Rearrange array elements by signLeetCode
Print the matrix in spiral mannerLeetCode
Pascal's Triangle ILeetCode
Pascal's Triangle IILeetCode
Pascal's Triangle III
Rotate matrix by 90 degreesLeetCode
Set Matrix ZeroesLeetCode
Two SumLeetCode
3 SumLeetCode
4 SumLeetCode
Sort an array of 0's 1's and 2'sLeetCode
Kadane's AlgorithmLeetCode
Next PermutationLeetCode

Majority Element-IILeetCode
Find the repeating and missing number
Count Inversions
Reverse PairsLeetCode
Maximum Product Subarray in an ArrayLeetCode
Merge two sorted arrays without extra space

Search X in sorted arrayLeetCode
Lower Bound
Upper Bound
Search insert positionLeetCode
Floor and Ceil in Sorted Array
First and last occurrenceLeetCode
Count Occurrences in a Sorted Array

Search in rotated sorted array-ILeetCode
Search in rotated sorted array-IILeetCode
Find minimum in Rotated Sorted ArrayLeetCode
Find out how many times the array is rotated
Single element in sorted arrayLeetCode
Find square root of a numberLeetCode
Find Nth root of a number
Find the smallest divisorLeetCode
Koko eating bananasLeetCode
Minimum days to make M bouquetsLeetCode
Capacity to Ship Packages Within D DaysLeetCode
Kth Missing Positive NumberLeetCode
Find peak elementLeetCode
Find row with maximum 1's
Search in a 2D MatrixLeetCode
Search in 2D matrix - IILeetCode

Painter's Partition
Aggressive Cows
Book Allocation Problem
Median of 2 sorted arraysLeetCode
Kth element of 2 sorted arrays
Minimize Max Distance to Gas StationLeetCode
Split array - largest sumLeetCode
Find Peak Element - IILeetCode
Matrix Median

Remove Outermost ParenthesesLeetCode
Maximum Nesting Depth of the ParenthesesLeetCode
Roman to IntegerLeetCode

String to Integer (atoi)LeetCode
Count Number of Substrings
Longest Palindromic SubstringLeetCode
Sum of Beauty of All SubstringsLeetCode
Reverse every word in a stringLeetCode
Minimum number of bracket reversals to make an expression balanced
Count and sayLeetCode

Rabin Karp Algorithm
Z function
KMP Algorithm or LPS array
Shortest PalindromeLeetCode
Longest happy prefixLeetCode

Introduction to Singly LinkedList
Traversal in Linked List
Deletion in Linked List
Insertion in Linked List
Deletion of the head of LL
Deletion of the tail of Linked List
Deletion of the Kth element of Linked List
Delete the element with value X
Insertion at the head of Linked List
Insertion at the tail of Linked List
Insertion at the Kth position of Linked List
Insertion before the value X in Linked List
Find the length of the Linked List
Search in Linked List
Introduction to Doubly LL
Deletion in Doubly LL
Insertion in DLL
Convert Array to Doubly Linked List
Delete head of Doubly Linked List
Delete Tail of Doubly Linked List
Delete Kth Element of Doubly Linked List
Removing given node in Doubly Linked List
Insert node before head in Doubly Linked List
Insert node before tail in Doubly Linked List
Insert node before (kth node) in Doubly Linked List
Insert before given node in Doubly Linked List

Reverse a Doubly Linked List
Delete all occurrences of a key in DLL
Remove duplicates from sorted DLL
Find Pairs with Given Sum in Doubly Linked List
Add two numbers in Linked ListLeetCode
Segregate odd and even nodes in Linked ListLeetCode
Sort a Linked List of 0's 1's and 2's
Remove Nth node from the back of the LLLeetCode
Reverse a LLLeetCode
Add one to a number represented by LL
Find Middle of Linked ListLeetCode
Delete the middle node in LLLeetCode
Check if LL is palindrome or notLeetCode
Find the intersection point of Y LLLeetCode
Detect a loop in LLLeetCode
Find the starting point in LLLeetCode
Length of loop in LL

Reverse LL in group of given size KLeetCode
Rotate a LLLeetCode
Merge two Sorted ListsLeetCode
Flattening of LL
Sort LLLeetCode
Clone a LL with random and next pointerLeetCode

Implementation using different DS

Implement Stack using Arrays
Implement Queue using Arrays
Implement Stack using QueueLeetCode
Implement Queue using StackLeetCode
Implement stack using Linkedlist
Implement queue using Linkedlist
Balanced ParanthesisLeetCode

Infix to Postfix Conversion
Infix to Prefix Conversion
Prefix to Infix Conversion
Prefix to Postfix Conversion
Postfix to Infix Conversion
Postfix to Prefix Conversion
Next Greater ElementLeetCode
Next Greater Element - 2LeetCode
Asteroid CollisionLeetCode
Sum of Subarray MinimumsLeetCode
Sum of Subarray RangesLeetCode
Remove K DigitsLeetCode
Next Smaller Element
Implement Min StackLeetCode
Stock span problemLeetCode
Celebrity Problem

Sliding Window MaximumLeetCode
Trapping RainwaterLeetCode
Largest rectangle in a histogramLeetCode
Maximum RectanglesLeetCode
LRU CacheLeetCode
LFU CacheLeetCode
Number of Greater Elements to the Right

Maximum Points You Can Obtain from CardsLeetCode
Longest Substring Without Repeating CharactersLeetCode
Max Consecutive Ones IIILeetCode
Fruit Into BasketsLeetCode
Longest Substring With At Most K Distinct CharactersLeetCode
Longest Repeating Character ReplacementLeetCode
Binary Subarrays With SumLeetCode
Count number of Nice subarraysLeetCode

Minimum Window SubstringLeetCode
Minimum Window SubsequenceLeetCode
Number of Substrings Containing All Three CharactersLeetCode
Subarrays with K Different IntegersLeetCode

Remove duplicates from sorted arrayLeetCode
Move Zeros to EndLeetCode
Union of two sorted arrays

Two SumLeetCode
3 SumLeetCode
Sort an array of 0's 1's and 2'sLeetCode

4 SumLeetCode
Merge two sorted arrays without extra space
Trapping RainwaterLeetCode

Heaps (Theory Video)

Heapify Algorithm
Build heap from a given Array
Implement Min Heap
Implement Max Heap
Check if an array represents a min heap
Convert Min Heap to Max Heap

Heap Sort
K-th Largest element in an arrayLeetCode
Kth largest element in a stream of running integersLeetCode
Sort K sorted array
Replace Elements by Their Rank
Task SchedulerLeetCode
Hand of StraightsLeetCode
Minimum Cost to Connect SticksLeetCode
Top K Frequent ElementsLeetCode

Merge K sorted ListsLeetCode
Design TwitterLeetCode
Maximum Sum Combination
Find Median from Data StreamLeetCode

Assign CookiesLeetCode
Lemonade ChangeLeetCode
Fractional Knapsack
Jump Game - ILeetCode
Shortest Job First

Job sequencing Problem
N meetings in one room
Non-overlapping IntervalsLeetCode
Insert IntervalLeetCode
Merge IntervalsLeetCode
Minimum number of platforms required for a railway
Valid Paranthesis Checker
Jump Game IILeetCode

CandyLeetCode

Introduction
Inorder TraversalLeetCode
Preorder TraversalLeetCode
Postorder TraversalLeetCode
Maximum Depth in BTLeetCode
Check if two trees are identical or notLeetCode
Check for balanced binary treeLeetCode
Diameter of Binary TreeLeetCode
Check for symmetrical BTsLeetCode

Level Order TraversalLeetCode
Pre, Post, Inorder in one traversal
Children Sum Property in Binary Tree
Zig Zag or Spiral TraversalLeetCode
Boundary Traversal
Vertical Order TraversalLeetCode
Top View of BT
Bottom view of BT
Right/Left View of BTLeetCode
Print root to leaf path in BTLeetCode
LCA in BTLeetCode
Maximum Width of BTLeetCode
Count total nodes in a complete BTLeetCode
Flatten Binary Tree to Linked ListLeetCode
Requirements needed to construct a unique BT

Maximum path sumLeetCode
Print all nodes at a distance of K in BTLeetCode
Minimum time taken to burn the BT from a given NodeLeetCode
Construct a BT from Preorder and InorderLeetCode
Construct a BT from Postorder and InorderLeetCode
Serialize and De-serialize BTLeetCode
Morris Inorder Traversal
Morris Preorder Traversal

Introduction to BST
Search in BSTLeetCode
Floor and Ceil in a BST
Find Min/Max in BST

Insert a given node in BSTLeetCode
Delete a node in BSTLeetCode
Kth Smallest and Largest element in BSTLeetCode
Check if a tree is a BST or notLeetCode
LCA in BSTLeetCode
Construct a BST from a preorder traversalLeetCode
Inorder successor and predecessor in BST
BST iteratorLeetCode
Two sum in BSTLeetCode

Correct BST with two nodes swappedLeetCode
Largest BST in Binary TreeLeetCode

Introduction to Graph
Traversal Techniques
Connected Components
Number of provincesLeetCode
Number of islandsLeetCode
Flood fill algorithmLeetCode

Number of enclavesLeetCode
Rotten OrangesLeetCode
Distance of nearest cell having oneLeetCode
Surrounded RegionsLeetCode
Number of distinct islands
Detect a cycle in an undirected graph
Bipartite graphLeetCode
Topological sort or Kahn's algorithm
Detect a cycle in a directed graph
Find eventual safe statesLeetCode
Course Schedule ILeetCode
Course Schedule IILeetCode
Shortest path in DAG
Shortest path in undirected graph with unit weights
Word ladder ILeetCode
Dijkstra's algorithm
Print Shortest Path
Shortest Distance in a Binary Maze
Path with minimum effortLeetCode
Cheapest flight within K stopsLeetCode
Minimum multiplications to reach end
Number of ways to arrive at destinationLeetCode
Bellman ford algorithm
Floyd warshall algorithm
Find the city with the smallest number of neighborsLeetCode
Network Delay TimeLeetCode
Swim in Rising WaterLeetCode

Alien DictionaryLeetCode
Word ladder IILeetCode
MST theory
Disjoint Set
Find the MST weight
Number of operations to make network connectedLeetCode
Accounts mergeLeetCode
Number of islands IILeetCode
Making a large islandLeetCode
Most stones removed with same row or columnLeetCode
Kosaraju's algorithm
Bridges in graphLeetCode
Articulation point in graph

Introduction to DP
Climbing stairsLeetCode
Frog Jump
Frog jump with K distances
Maximum sum of non adjacent elements
House robberLeetCode
Grid unique pathsLeetCode
Unique paths IILeetCode
Best time to buy and sell stockLeetCode

Ninja's training
Minimum Falling Path SumLeetCode
TriangleLeetCode
Count Square Submatrices with All OnesLeetCode
Best time to buy and sell stock IILeetCode
Best time to buy and sell stock with transaction feesLeetCode
Best Time to Buy and Sell Stock with CooldownLeetCode
Subset sum equals to target
Partition equal subset sumLeetCode
Partition a set into two subsets with minimum absolute sum difference
Count subsets with sum K
Count partitions with given difference
0 and 1 Knapsack
Minimum coinsLeetCode
Target sumLeetCode
Coin change IILeetCode
Unbounded knapsack
Rod cutting problem
Longest Increasing SubsequenceLeetCode
Print Longest Increasing Subsequence
Largest Divisible SubsetLeetCode
Longest String ChainLeetCode
Longest Bitonic Subsequence
Longest common subsequenceLeetCode
Longest common substringLeetCode
Longest palindromic subsequenceLeetCode
Minimum insertions to make string palindromeLeetCode
Minimum insertions or deletions to convert string A to BLeetCode
Shortest common supersequenceLeetCode
Edit distanceLeetCode
Word BreakLeetCode
Count Palindromic Subsequences

Cherry pickup IILeetCode
Best time to buy and sell stock IIILeetCode
Best time to buy and sell stock IVLeetCode
Number of Longest Increasing SubsequencesLeetCode
Distinct subsequencesLeetCode
Wildcard matchingLeetCode
Matrix chain multiplication
Burst balloonsLeetCode
Palindrome partitioning IILeetCode
Partition Array for Maximum SumLeetCode
Minimum cost to cut the stickLeetCode
Different Ways to Evaluate a Boolean Expression

Power SetLeetCode
Count Good NumbersLeetCode

Subsets ILeetCode
Subsets IILeetCode
Combination SumLeetCode
Combination Sum IILeetCode
Combination Sum IIILeetCode
Letter Combinations of a Phone NumberLeetCode
Palindrome partitioningLeetCode
Word SearchLeetCode
Rat in a Maze

N QueenLeetCode
M Coloring Problem
Sudoku SolverLeetCode
Expression Add OperatorsLeetCode

Create a Student class and print details
Class Rectangle with area()
Counter class with increment()

BankAccount with deposit/withdraw rules
Immutable Point class
Library book issue/return

Design a parking lot (classes only)
Matrix class with add/multiply
Polynomial class with add/multiply

Default constructor demo
Parameterised constructor for Employee
Constructor overloading

Constructor chaining with this()
Copy constructor
Singleton with private constructor

Builder pattern for a complex object
Thread-safe singleton
Immutable class with defensive copy

Private fields with getters/setters
Validate age in setter
Read-only property

Encapsulated BankAccount with PIN
Package-private vs protected demo
Employee with salary validation

Immutable class with mutable field inside
Design a secure wallet class
Access modifier matrix across packages

Animal → Dog example
Use super() to call parent constructor
Multilevel inheritance

Shape hierarchy with area()
Method hiding vs overriding
Employee → Manager → Director

Diamond problem and how Java avoids it
Design an inheritance-based vehicle system
Composition vs inheritance refactor

Method overloading for add()
Override toString()
Parent reference to child object

Dynamic dispatch with Shape[]
Overloading with null / ambiguity
Covariant return types

Double dispatch / visitor pattern
Predict output of tricky override + overload code
Polymorphic payment system

Abstract Shape with area()
Abstract class with concrete method
Instantiate via subclass

Template method pattern
Abstract class with constructor
Abstract vs concrete method order of calls

Design a plugin system with abstract base
Abstract factory pattern
Refactor duplicated code into abstract base

Implement a simple interface
Implement two interfaces
Interface constants

Default method conflict resolution
Functional interface with lambda
Strategy pattern with interface

Design a notification system with interfaces
Static and private interface methods
Sealed interfaces with records

Handle ArithmeticException
try/catch/finally flow
Handle ArrayIndexOutOfBounds

Custom checked exception
try-with-resources
Multi-catch and rethrow

Exception chaining with cause
finally vs return puzzle
Design a retry mechanism with custom exceptions

Generic Box<T>
Generic method to print any array
Generic Pair<K,V>

Bounded type parameters
Wildcards (? extends / ? super)
Generic stack implementation

Type erasure pitfalls
Generic LRU cache
PECS principle with a copy() method

Write text to a file
Read a file line by line
Append to a file

Copy a file using streams
Word count of a file
Serialise and deserialise an object

Log file analyser (top IPs)
Merge sorted large files
Simple CSV parser with error handling

Static counter shared by objects
Enum for days of week
Autoboxing and unboxing demo

Implement equals/hashCode and use in HashSet
Sort with Comparable and Comparator
Filter and map a list using Streams

Group by and count using Collectors
Custom collector or parallel stream pitfalls
Design an immutable value class with records

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