iamsrirams / DSA_Java

📂 Data Structures and Algorithms in Java

Note:

• The best way to prepare would be to clone this repo and mark the problems as completed as you progress along.
• If you're interested in explanations, check out DSA_Kotlin Repo, which has video explanations for every problem in this problem set.

Topics:

• Arrays
• Trees
• Linked List
• Stack
• Queue
• Dynamic Programming
• Greedy Problems
• Divide and Conquer
• Bit Manipulation
• Mathematical
• Hashing
• String
• Pattern Matching
• Heaps
• Back Tracking
• Graphs

Array Problems

• One -> Linear Search
• Two -> Binary Search
• Three -> Find a pair in an array whose sum is equal to given number (Hash Approach) - Brute Force, Quick Sort and search complement, Hash Table
• Four -> Element that occurs more than n/2 times - Unsorted
• Five -> Element that occurs more than n/2 times - Sorted
• Six -> Largest Difference such that the smaller number appears before larger number
• Seven -> Largest Difference such that the smaller number appears before larger number - Less space complexity
• Eight -> Largest Difference such that the smaller number appears before larger number - Min So Far
• Nine -> Find the number occurring odd number of times in the given array(Only one element occurs odd number of times)
• Ten -> Separate 0's and 1's in an array
• Eleven -> Separate Even and Odd numbers in an array
• Twelve -> 2 elements whose sum is close to zero - either positive or negative
• Thirteen -> 3 elements such that their sum is equal to x.
• Fourteen -> Find the Equilibrium Index .i.e., left sum and right sum of index should be equal.
• Fifteen -> Find the Equilibrium Index .i.e., left sum and right sum of index should be equal - Less Space Complexity.
• Sixteen -> Array of unknown size. 0s followed by 1s find the first index of 1
• Seventeen -> Maximum of every contiguous sub-array of size k. - Sliding Window.
• Eighteen -> count the no.of smaller elements to the right of each element in the array.
• Nineteen -> Largest Multiple of 3 with given digits.
• Twenty -> Sub Array Sum equal to x
• TwentyOne -> Find Sub Array whose sum is equals zero
• TwentyTwo -> Largest sub array with equal no.of zeros and ones
• TwentyThree -> Construct a product array such that the ith element in product array contains the product of all the remaining elements but i (Without Division)
• TwentyFour -> Construct a product array such that the ith element in product array contains the product of all the remaining elements but i (Without Division) - less time complexity
• TwentyFive -> Sort a nearly sorted array, each element can be misplaced by a max of k digits before or after
• TwentySix -> Find Duplicates in O(n) time and O(1) space - Array element values are ≤ Max Index
• TwentySeven -> Find 2 repeating elements in a given array - XOR - Given (n+2) elements - 1 ≤ a[i] ≤ n - All elements from 1 to n occurs at least once (Except the 2 numbers that occurs twice)
• TwentyEight -> Rotate an array of size n by d elements - Left rotation - Beginning to End - Juggling Algorithm
• TwentyNine -> Sort array in wave form - Even position number
• Thirty -> Next least greater number to the given number, input as digit array - with same digits
• ThirtyOne -> Trapping Rain Water Problem
• ThirtyTwo -> No.of Triangles that can be formed
• ThirtyThree -> Smallest number that can't be formed from the array of given numbers
• ThirtyFour -> Rearrange such that a[i] becomes a[a[i]]
• ThirtyFive -> Rotate Matrix by 90 degree - anti-clockwise
• ThirtySix -> Count number of occurrences (or frequency) in a sorted array
• ThirtySeven -> Find Sub Array whose sum is equals zero - reduced time complexity
• ThirtyEight -> Largest sub array with equal no.of zeros and ones - my way

Tree Problems

• One -> Size of a Binary Tree
• Two -> Identical or not
• Three -> Mirror Tree
• Four -> Level Order Traversal
• Five -> Lowest Common Ancestor (LCA) - BST
• Six -> Lowest Common Ancestor (LCA) - Binary Tree
• Seven -> Binary Tree into DLL - IN order - InPlace conversion
• Eight -> Diameter of the Binary Tree
• Nine -> Find the level of a given node
• Ten -> Print nodes at k distance form root
• Eleven -> Print nodes at K distance form any node in BT
• Twelve -> Vertical Tree Order Traversal
• Thirteen -> Vertical Sum of the Binary Tree
• Fourteen -> Sum Tree or not
• Fifteen -> Top View
• Sixteen -> Bottom View
• Seventeen -> Left View
• Eighteen -> Remove all paths whose length < K in BT.
• Nineteen -> One BT is a sub tree of another BT or not
• Twenty -> Cousin Nodes or not
• TwentyOne -> Balanced BST construction from a sorted List
• TwentyTwo -> BST into Balanced BST
• TwentyThree -> Print all paths possible from root to all leaves
• TwentyFour -> Spiral Level Order Traversal
• TwentyFive -> BT construction from the given POST and IN Order
• TwentySix -> All nodes at K distance from leaf
• TwentySeven -> Expression Evaluation
• TwentyEight -> Extreme nodes of each level in alternating order
• TwentyNine -> Diagonal Traversal BT
• Thirty -> BT to a BT that holds Child sum property
• ThirtyOne -> Multiplication of Sums of data of leaves at same level
• ThirtyTwo -> Multiplication of Sums of data at same level
• ThirtyThree -> Max of all differences of a node and it's ancestors BT
• ThirtyFour -> Serialization and Deserialization BT
• ThirtyFive -> Serialization and Deserialization n-ary Tree
• ThirtySix -> Tree from ancestor Matrix
• ThirtySeven -> Complete Binary Tree from a LL
• ThirtyEight -> Find the next right node of a given node in the same level
• ThirtyNine -> Boundary Traversal
• Forty -> Convert a given tree into sum tree
• FortyOne -> Check if Foldable or not
• FortyTwo -> Check if removing an edge will cut into two equal halves
• FortyThree -> Locking and Unlocking a Node - Design Problem
• FortyFour -> Reverse Alternate Levels of a perfect BT
• FortyFive -> Custom Tree Print Problem
• FortySix -> Threaded BT

Linked List Problems

• One -> Reverse a LL
• Two -> Middle of a LL
• Three -> Kth node from the end of the LL
• Four -> Detect loop in LL
• Five -> Find the start of the Loop in the LL with Loop
• Six -> 2 LL merge at a point, find that point
• Seven -> Alternating Split
• Eight -> Clone a LL that contains Random Pointer (Custom LL)
• Nine -> Palindrome of a LL
• Ten -> Merge 2 Sorted LL into one Sorted LL
• Eleven -> Merge K sorted LL of size N into single Sorted LL of size kn
• Twelve -> Merge sort on LL
• Thirteen -> LL with arb-pointer pointing to greatest in the right side of the current node
• Fourteen -> Memory efficient DLL
• Fifteen -> Sort a LL with 0s, 1s and 2s
• Sixteen -> Add 1 to number represented as LL
• Seventeen -> Merge K sorted LL of size N into single Sorted LL of size kn - Better complexity

Stack Problems

• One -> Stack using Queues
• Two -> getMin @ O(1)
• Three -> Reverse a Stack
• Four -> closest greater element to the right
• Five -> Overlapping Intervals
• Six -> Balancing Parenthesis
• Seven -> Stock Span Problem
• Eight -> Min no.of bracket reversals req to make the eqn balanced
• Nine -> find duplicate parenthesis present or not
• Ten -> Celebrity Problem

Queue Problems

• One -> Circular tour that visit all gasoline stations before running out of gas

Dynamic Programming

• One -> Maximum Sum Sub array
• Two -> Maximum Sum Increasing Sub Sequence [OR] Longest increasing Sub Sequence
• Three -> Longest Sub Sequence in an array such that the element are consecutive
• Four -> In a Binary Matrix, Max Square Matrix with all 1s
• Five -> Kth Ugly Number
• Six -> Longest Increasing Sub Sequence
• Seven -> Longest Decreasing Sub Sequence
• Eight -> Perfect Hill Sequence
• Nine -> Edit Distance
• Ten -> Largest Sum Independent set in a Binary Tree
• Eleven -> Find n-bit integer that doesn't have 2 consecutive zeros
• Twelve -> Word breaking problem
• Thirteen -> Partition Problem - Sub Set Sum Problem
• Fourteen -> Longest Palindromic sub sequence
• Fifteen -> Steps 1 or 2 to reach n
• Sixteen -> Longest non overlapping repeating sub string
• Seventeen -> Min cost to make strings(x and y) equal, del(x) -> S, del(y) -> P
• Eighteen -> No.of times a string appeared as Sub Sequence in other string
• Nineteen -> No.of ways to fill 2xn with 2x1
• Twenty -> Given a Cost matrix, min cost to reach (m-1,n-1) from (0,0), allowed movements -> left, right, diagonally down
• TwentyOne -> K palindrome - If string becomes palindrome or not by doing atmost k deletions
• TwentyTwo -> Longest Common Sub Sequence
• TwentyThree -> Sum of all digits from 1 to n
• TwentyFour -> Given a string of digits, sub string length = 2k, sum of left k = sum of right k
• TwentyFive -> Given a BT, find Largest Independent Set
• TwentySix -> Cutting Rod
• TwentySeven -> Longest Palindromic sub string
• TwentyEight -> Count all Palindromic sub string in a string
• TwentyNine -> Count all distinct Palindromic sub string in a string
• Thirty -> Rectangular grid 2xn, max sum such that no 2 chosen digit are adj -> vertically, horizontally, diagonally
• ThirtyOne -> Arrays A -> m, B -> n, (m>n) insert(m-n) 0s in B such that dot product is max
• ThirtyTwo -> Largest Independent Set
• ThirtyThree -> Egg Dropping Problem
• ThirtyFour -> No.of Non-decreasing numbers with n digits
• ThirtyFive -> Weighted Job Scheduling
• ThirtySix -> Count no.of ways to reach a score in a given game, player can score 2, 4 or 6 points
• ThirtySeven -> Max coins by busting balloons
• ThirtyEight -> Max points in the grid using 2 traversals
• ThirtyNine -> Sub Set Sum Problem
• Forty -> Matrix Chaining - Results Upper triangular Matrix
• FortyOne -> Longest Common Sub Sequence
• FortyTwo -> Multi Stage Graph
• FortyThree -> 0/1 Knapsack
• FortyFour -> Travelling Sales man (TSP) - DFS based - Hamiltonian Cycle + MIN Cost
• FortyFive -> All Pair Shortest path - Floyd Warshall's
• FortySix -> Matrix Chaining - Top Down
• FortySeven -> Coin Change Problem
• FortyEight -> Longest Palindromic sub string - Less Space Complexity
• FortyNine -> No.of Non-decreasing numbers with n digits - Less space

Greedy Problems

• One -> n different ropes of different length, tie them up into a single rope with Min cost.
• Twp -> Maximum Non Overlapping Intervals
• Three -> Min no.of platforms required to station all trains without collision
• Four -> Rearrange the characters in the string such that same characters become d-distance away from each other.
• Five -> Dijkstra's Algorithm
• Six -> Fractional Knapsack
• Seven -> Huffman's Coding
• Eight -> Job Sequencing with Deadlines
• Nine -> Spanning Trees and kirchhoff's theorem
• Ten -> Minimum Spanning Tree - Prim's
• Eleven -> Kruskal's Algorithm
• Twelve -> Optimal Merge Patterns

Divide and Conquer

• One -> Find the element that occurs more than n/2 times - Sorted Array.
• Two -> Bolt and Nuts
• Three -> Implement pow()
• Four -> Search an element in a sorted Rotated Array
• Five -> Count Inversions in an array
• Six -> Missing number in arithmetic progression
• Seven -> Array containing 0s before 1s, count 1s
• Eight -> Array has 2n elements -> a1, a2, a3, .., an, b1, b2, .. , bn -> shuffle -> a1, b1, a2, b2, .., an, bn
• Nine -> Sorted Array of non-repeating elements, find if there's i for which a[i] = i
• Ten -> a[0]..a[i] -> increasing, a[i+1]..a[n] -> decreasing, find i
• Eleven -> search for an element in a row-wise and column-wise sorted 2d array.
• Twelve -> External Sorting
• Thirteen -> Find median of 2 sorted arrays
• Fourteen -> Find Peek Element
• Fifteen -> Get first 1.

Bit Manipulation

• One -> Kth bit is set or not
• Two -> set Kth Bit of a number
• Three -> clear Kth bit of a number
• Four -> Toggle Kth bit of a number
• Five -> count the no.of set bits of a number
• Six -> power of 2 or not
• Seven -> next higher number of the given number which is a power of 2
• Eight -> power of 4 or not
• Nine -> Multiply with 7 without using *
• Ten -> Check if a Number is Odd or Even using Bitwise Operators

Mathematical

• One -> Prime or not
• Two -> Print prime upto n - Sieve of Eratosthenes Algorithm
• Three -> Lucky number or not

Hashing

• One -> check if the array has duplicate entries at K distance or not
• Two -> check if 2 sets are disjoint or not
• Three -> Group all occurrences of elements order by their 1st occurrence.
• Four -> Given an array A, count the distinct elements in all windows of size K
• Five -> Given an array and a range (low, high). Find the elements that are in the range but not in the array.
• Six -> Find the no.of sub arrays with sum zero
• Seven -> Find 4 elements i, j, k & l -> such that i + j = k + l

Strings

• One -> Find a max occurring character in a given array.
• Two -> Remove duplicates in a given string
• Three -> Check if given 2 strings are rotations of each other
• Four -> Reverse the words in the given sentence
• Five -> Reverse a given string
• Six -> Check if palindrome
• Seven -> Find 1st non-repeating character in the given string
• Eight -> Run length encoding
• Nine -> Anagrams
• Ten -> Excel column name for a given excel column number (MS Excel)
• Eleven -> Find a smallest window in a string containing all characters of another string
• Twelve -> Find 1s non-repeating character in a stream of characters
• Thirteen -> All combinations of strings used to dail a number (Old Phone Key pad)
• Fourteen -> Min no.of palindromic sub-sequences to be removed to empty a binary string
• Fifteen -> Check if given sequence of moves for robot is circular or not
• Sixteen -> Min and Max of an array using min no.of comparisons
• Seventeen -> Convert one string to another using min no.of given operations
• Eighteen -> Print concatenation of zig-zack string in k-rows
• Nineteen -> Remove adj duplicate characters in a given string
• Twenty -> Min no.of palindromic sub-sequences to be removed to empty a binary string - Tournament Method

Pattern Matching

• One -> Find all occurrences of str2 in str1 - Brute force
• Two -> Knuth Morris Pratt Algorithm
• Three -> Boyer's Moore String Matching Algorithm
• Four -> Rabin-Karp String Matching Algorithm
• Five -> Find all occurrences of a given word in a matrix

Heaps

• One -> Finding the max element in MIN heap
• Two -> Deleting arb element in MIN heap
• Three -> K-Largest elements from an array
• Four -> Median in a stream of numbers
• Five -> Given K-sorted list, find minimum range to which at least on number belongs from every list. - All list are of same size
• Six -> Convert MAX heap into MIN Heap
• Seven -> Print out all integers of the form a^3+b^3 where a & b are integers b/w 0 & n in sorted order.
• Eight -> Convert BST to MAX Heap
• Nine -> Find the Kth largest element in a stream
• Ten -> Tournament Tree
• Eleven -> Print all elements in sorted order in row wise and column wise sorted matrix
• Twelve -> Sort a nearly sorted array
• Thirteen -> Given n ropes with different length, connect with minimum cost.
• Fourteen -> Check if the given binary tree is a max heap or not.
• Fifteen -> Given K-sorted arrays of size n-each, merge them. - different sized inner lists
• Sixteen -> Delete root from a heap.

Back Tracking

• One -> Print all permutations of given string
• Two -> Print all the strings of n-bits
• Three -> N-Queens Problem
• Four -> Rat in Maze
• Five -> Knight Tour Problem
• Six -> Find subset of elements that are selected from a given set whose sum adds upto a given number k // Subset Sum Problem - Using Backtracking
• Seven -> SUDOKU
• Eight -> N-Queens Problem - Easy way

Graph Problems

• One -> DFS
• Two -> BFS
• Three -> Find if there's a path between vi and vj in a directed graph
• Four -> Undirected Graph, cycle or not
• Five -> Bipartite or not
• Six -> Detect a cycle in a directed graph
• Seven -> Print all jumping numbers smaller than or equal to given value(k)
• Eight -> Single source shortest path - DAG
• Nine -> Longest Path in DAG, no weights
• Ten -> Find Articulation Point / Cut Vertex, Undirected
• Eleven -> Longest Path in DAG, with weights