Data Structure and Algorithmic Problems

This repository consists of my solution of algorithm and data structures problems in different online judge platforms i.e LeetCode, Hackerrank, UVA, CodeForces, GFG. 80% of the problems have been solved using Java, rest are C and C++.

Although I solved many more problems in these platforms, I only documented these solutions.

List of problems

All the problems are categorized by the respective online judge. You can access the problem and the solution directly from the link.

Geeks for Geeks (GFG)

Practice problems from Geek for Geek in Java. All the codes are tested in online-judge. Some problems are not solved yet.

• Mathematical and Algorithmic Puzzle

  • Easy

    • GCD of Array
    • Sum of all prime numbers between 1 and N
    • Pairs of prime number
    • Pair cube count
    • Check if given four points form a square
    • Perfect Numbers
    • Print the Kth Digit
    • Closest Number
    • Series GP
    • Add two fractions
    • Find Nth root of M
    • Trailing zeroes in factorial
    • Triangular Number
    • Overlapping rectangles
    • Number Of Open Doors
    • Angle between hour and minute hand
    • Day of the week
    • 3 Divisors
    • Count Squares
    • Nth Even Fibonacci Number
    • Squares in a Matrix

  • Medium

    • Last two digits of Fibonacci
    • Largest prime factor
    • nCr
    • Jumping Numbers

  • Contest

    • Unit Digit

• Array

  • Easy

    • Rotate Array
    • Remove Duplicates from unsorted array
    • Find minimum and maximum element in an array
    • Minimum distance between two numbers
    • Operating an array
    • Chocolate Distribution Problem
    • Count Smaller elements
    • Majority Element
    • Sorted subsequence of size 3
    • Leaders in an array
    • Max sum path in two arrays
    • Product array puzzle
    • Find duplicates in an array
    • Longest Consecutive Subsequence
    • Three way partitioning
    • Wave Array
    • Pair with given sum in a sorted array

  • Medium

    • Trapping Rain Water
    • Stock buy and sell
    • Maximum Sub Array
    • Find Missing And Repeating
    • Maximum Index

  • Contest

    • Ups and Downs
    • alternating-elements

• Backtracking

  • Easy

    • Permutations of a given string

  • Medium

LeetCode

Solved problems from Leetcode using Java. All the codes are tested in online-judge.

Easy

#	Title	Tag
1	Two Sum	Array, Hash Table
7	Reverse Integer	Math
9	Palindrome Number	Math
13	Roman to Integer	Math, String
14	Longest Common Prefix	String
20	Valid Parentheses	String, Stack
21	Merge Two Sorted Lists	Linked List
26	Implement strStr()	String
26	Remove Duplicates from Sorted Array	Array, Two Pointers
27	Remove Element	Array, Two Pointers
35	Search Insert Position	Binary Search
53	Maximum Subarray	Array
58	Length of Last Word	String
67	Add Binary	String
69	Sqrt(x)	Binary Search
83	Remove Duplicates from Sorted List	Linked List
88	Merge Sorted Array	Array, Two Pointers
100	Same Tree	Tree
101	Symmetric Tree	Tree
104	Maximum Depth of Binary Tree	Tree
107	Binary Tree Level Order Traversal II	Tree
108	Convert Sorted Array to Binary Search Tree	Tree
110	Balanced Binary Tree	Tree
111	Minimum Depth of Binary Tree	Tree
112	Path Sum	Tree
118	Pascal's Triangle	Array
121	Best Time to Buy and Sell Stock	Array, Dynamic Programming
125	Valid Palindrome	String
136	Single Number	Hash Table, Bit Manipulation
141	Linked List Cycle	Linked List
155	Min Stack	Stack
160	Intersection of Two Linked Lists	Linked List
167	Two Sum II - Input array is sorted	Array, Two Pointers, Binary Search
189	Rotate Array	Array
203	Remove Linked List Elements	Linked List
205	Isomorphic Strings	Hash Table
206	Reverse Linked List	Linked List
215	Kth Largest Element in an Array	Heap
217	Contains Duplicate	Hash Table
219	Contains Duplicate II	Array, Hash Table
225	Implement Stack using Queues	Stack
226	Invert Binary Tree	Tree
232	Implement Queue using Stacks	Stack
234	Palindrome Linked List	Linked List
235	Lowest Common Ancestor of a Binary Search Tree	Tree
237	Delete Node in a Linked List	Linked List
242	Valid Anagram	Hash Table, Sort
257	Binary Tree Paths	Tree
268	Missing Number	Array, Math, Bit Manipulation
278	First Bad Version	Array
283	Move Zeroes	Array, Two Pointers
290	Word Pattern	Hash Table
344	Reverse String	String
345	Reverse Vowels of a String	String
349	Intersection of Two Arrays	Hash Table, Sort, Two Pointers, Binary Search
350	Intersection of Two Arrays II	Hash Table, Sort, Two Pointers
367	Valid Perfect Square	Binary Search
383	Ransom Note	String
387	First Unique Character in a String	String
401	Binary Watch	Backtracking
404	Sum of Left Leaves	Tree
414	Third Maximum Number	Array
415	Add Strings	String
429	N-ary Tree Level Order Traversal	Tree
434	Number of Segments in a String	String
437	Path Sum III	Tree
443	String Compression	String
448	Find All Numbers Disappeared in an Array	Array
459	Repeated Substring Pattern	String
463	Island Perimeter	Hash Table
485	Max Consecutive Ones	Array, Two Pointers
496	Next Greater Element I	Stack
500	Keyboard Row	Hash Table
501	Find Mode in Binary Search Tree	Tree
509	Fibonacci Number	Array, Math
520	Detect Capital	String
538	Convert BST to Greater Tree	Tree
541	Reverse String II	String
543	Diameter of Binary Tree	Tree
551	Student Attendance Record I	String
557	Reverse Words in a String III	String
559	Maximum Depth of N-ary Tree	Tree
563	Binary Tree Tilt	Tree
572	Subtree of Another Tree	Tree
575	Distribute Candies	Hash Table
589	N-ary Tree Preorder Traversal	Tree
590	N-ary Tree Postorder Traversal	Tree
617	Merge Two Binary Trees	Tree
637	Average of Levels in Binary Tree	Tree
645	Set Mismatch	Hash Table
653	Two Sum IV - Input is a BST	Tree
657	Robot Return to Origin	String
669	Trim a Binary Search Tree	Tree
680	Valid Palindrome II	String
682	Baseball Game	Stack
686	Repeated String Match	String
687	Longest Univalue Path	Tree
690	Employee Importance	Hash Table, Depth First Search
696	Count Binary Substrings	String
700	Search in a Binary Search Tree	Tree
703	Kth Largest Element in a Stream	Heap
704	Binary Search	Binary Search
705	Design HashSet	Hash Table
706	Design HashMap	Hash Table
707	Design Linked List	Linked List
709	To Lower Case	String
720	Longest Word in Dictionary	Trie
733	Flood Fill	Depth First Search
747	Largest Number At Least Twice of Others	Array
748	Shortest Completing Word	Hash Table
771	Jewels and Stones	HashTable
784	Letter Case Permutation	Backtracking
804	Unique Morse Code Words	String
811	Subdomain Visit Count	Hash Table
819	Most Common Word	String
824	Goat Latin	String
832	Flipping an Image	Array
844	Backspace String Compare	Stack
852	Peak Index in a Mountain Array	Binary Search
859	Buddy Strings	String
867	Transpose Matrix	Array
872	Leaf-Similar Trees	Tree
876	Middle of the Linked List	Linked List
884	Uncommon Words from Two Sentences	Hash Table
893	Groups of Special-Equivalent Strings	String
896	Monotonic Array	Array
897	Increasing Order Search Tree	Tree
905	Sort Array By Parity	Array
917	Reverse Only Letters	String, Two Pointers
922	Sort Array By Parity II	Array
925	Long Pressed Name	String
929	Unique Email Addresses	String
937	Reorder Log Files	String, Sorting
941	Valid Mountain Array	Array
944	Delete Columns to Make Sorted	Greedy
949	Largest Time for Given Digits	Math
953	Verifying an Alien Dictionary	Sorting
965	Univalued Binary Tree	Tree
970	Powerful Integers	Math
973	K Closest Points to Origin	Math
976	Largest Perimeter Triangle	Math, Sorting
978	Longest Turbulent Subarray	Array, Two Pointers, Sort
984	String Without AAA or BBB	Greedy
985	Sum of Even Numbers After Queries	Array
989	Add to Array-Form of Integer	Array
993	Cousins in Binary Tree	Tree
994	Rotting Oranges	Breadth First Search
997	Find the Town Judge	Graph
999	Available Captures for Rook	Array
1002	Find Common Characters	Array
1005	Maximize Sum Of Array After K Negations	Greedy
1012	Complement of Base 10 Integer	Math
1013	Partition Array Into Three Parts With Equal Sum	Array
1013	Pairs of Songs With Total Durations Divisible by 60	Array
1018	Binary Prefix Divisible By 5	Array
1022	Sum of Root To Leaf Binary Numbers	Tree
1030	Matrix Cells in Distance Order	Sort
1037	Valid Boomerang	Math

Medium

#	Title	Tag
2	Add Two Numbers	Linked List
8	String to Integer (atoi)	Math, String
11	Container With Most Water	Array
12	Integer to Roman	Math, String
17	Letter Combinations of a Phone Number	String, Backtracking
22	Generate Parentheses	String, Backtracking
34	Find First and Last Position of Element in Sorted Array	Array
43	Multiply Strings	String
46	Permutations	Backtracking
48	Rotate Image	Array
49	Group Anagrams	String
56	Merge Intervals	Array, Sort
75	Sort Colors	Two Pointers, Sorting
78	Subsets	Backtracking
94	Binary Tree Inorder Traversal	Tree
98	Validate Binary Search Tree	Tree
102	Binary Tree Level Order Traversal	Tree
103	Binary Tree Zigzag Level Order Traversal	Tree
105	Construct Binary Tree from Preorder and Inorder Traversal	Tree
106	Construct Binary Tree from Inorder and Postorder Traversal	Tree
113	Path Sum II	Tree
114	Flatten Binary Tree to Linked List	Tree
116	Populating Next Right Pointers in Each Node	Tree
117	Populating Next Right Pointers in Each Node II	Tree
129	Sum Root to Leaf Numbers	Tree
150	Evaluate Reverse Polish Notation	String, Stack
173	Binary Search Tree Iterator	Tree
207	Course Schedule	DFS, Topological Sort
208	Implement Trie (Prefix Tree)	Trie
210	Course Schedule II	DFS, Topological Sort
211	Add and Search Word - Data structure design	Trie
222	Count Complete Tree Nodes	Tree
227	Basic Calculator II	Stack, String
236	Lowest Common Ancestor of a Binary Tree	Tree
238	Product of Array Except Self	Array
287	Find the Duplicate Number	Binary Search
334	Increasing Triplet Subsequence	Array
341	Flatten Nested List Iterator	Stack, Design
347	Top K Frequent Elements	Heap, Hash Table
373	Find K Pairs with Smallest Sums	Heap
394	Decode String	Stack
442	Find All Duplicates in an Array	Array
445	Add Two Numbers II	Linked List
450	Delete Node in a BST	Tree
451	Sort Characters By Frequency	Heap, Hash Table
495	Teemo Attacking	Array
503	Next Greater Element II	Stack
508	Most Frequent Subtree Sum	Hash Table, Tree
513	Find Bottom Left Tree Value	Tree
515	Find Largest Value in Each Tree Row	Tree
524	Longest Word in Dictionary through Deleting	Two Pointers, String
525	Contiguous Array	Hash Table
526	Beautiful Arrangement	Backtracking
537	Complex Number Multiplication	String
539	Minimum Time Difference	String
547	Friend Circles	Union Find
609	Find Duplicate File in System	String
622	Design Circular Queue	Queue
623	Add One Row to Tree	Tree
641	Design Circular Deque	Queue
648	Replace Words	Trie
654	Maximum Binary Tree	Tree
676	Implement Magic Dictionary	Trie
677	Map Sum Pairs	Trie
692	Top K Frequent Words	Heap, Hash Table
695	Max Area of Island	Array, DFS
701	Insert into a Binary Search Tree	Tree
729	My Calendar I	Array
739	Daily Temperatures	Stack
785	Is Graph Bipartite?	DFS, BFS, Graph
791	Custom Sort String	String
802	Find Eventual Safe States	Depth First Search, Graph
833	Find And Replace in String	String
841	Keys and Rooms	Graph, DFS
848	Shifting Letters	String
875	Koko Eating Bananas	Array, Binary Search
881	Boats to Save People	Two Pointers
889	Construct Binary Tree from Preorder and Postorder Traversal	Tree
890	Find and Replace Pattern	String
900	RLE Iterator	Array
904	Fruit Into Baskets	Two pointers, Sliding Window
911	Online Election	Binary Search
916	Word Subsets	String
921	Minimum Add to Make Parentheses Valid	Stack
934	Shortest Bridge	Depth First Search, Breadth First Search
945	Minimum Increment to Make Array Unique	Array
946	Validate Stack Sequences	Stack
950	Reveal Cards In Increasing Order	Array, Queue
958	check-completeness-of-a-binary-tree	Tree
962	Maximum Width Ramp	Array
966	Vowel Spellchecker	String
978	Longest Turbulent Subarray	Array
981	Time Based Key-Value Store	Hash Table, Binary Search
988	Smallest String Starting From Leaf	Tree
998	Maximum Binary Tree II	Tree
1003	Check If Word Is Valid After Substitutions	Stack
1004	Max Consecutive Ones III	Two Pointers
1007	Minimum Domino Rotations For Equal Row	Array, Greedy
1008	Construct Binary Search Tree from Preorder Traversal	Tree
1014	Capacity To Ship Packages Within D Days	Array, Binary Search
1016	Binary String With Substrings Representing 1 To N	String
1019	Next Greater Node In Linked List	Linked List, Stack
1023	Camelcase Matching	String
1038	Binary Search Tree to Greater Sum Tree	Binary Search Tree

Hard

#	Title	Tag
42	Trapping Rain Water	Array, Two Pointers, Stack
224	Basic Calculator	Math, Stack, String

Hackerrank

Solved problems from Hackerrank using Java. All the codes are tested in online-judge.

Easy

Title	Tag
Minimum Absolute Difference in an Array	Array, Greedy
Luck Balance	Greedy
Strings: Making Anagrams	String
Arrays: Left Rotation	Arrays
Quicksort 1 - Partition	Sorting
Counting Sort 1	Sorting
Counting Sort 2	Sorting
Equal Stack	Stack
Detect a Cycle	Linked List
Reverse a doubly linked list	Linked List
Insert a node at a specific position in a linked list	Linked List
Inserting a Node Into a Sorted Doubly Linked List	Linked List
Find Merge Point of Two Lists	Linked List
Print the Elements of a Linked List	Linked List
Insert a Node at the Tail of a Linked List	Linked List
Insert a node at the head of a linked list	Linked List
Delete a Node	Linked List
Print in Reverse	Linked List
Reverse a linked list	Linked List
Merge two sorted linked lists	Linked List
Get Node Value	Linked List
Compare two linked lists	Linked List
Delete duplicate-value nodes from a sorted linked list	Linked List
Jesse and Cookies	Heap
QHEAP1	Heap
2D Array - DS	Array
Height of a Binary Tree	Tree

Medium

Title	Tag
Greedy Florist	Greedy
Max Min	Greedy
Balanced Brackets	Stack
Pairs	Search
The Full Counting Sort	Sorting, String
Queues: A Tale of Two Stacks	Stack
Cycle Detection	Linked List
Sparse Arrays	Arrays
Sorting: Comparator	Sorting
Is This a Binary Search Tree?	Trees

Hard

Title	Tag

UVA Online Judge

Solved problems from UVA using C, C++, Java. All the codes are tested in online-judge.

#	Title	Tag
119	Greedy gift givers
272	Tex quotes
290	Palindroms smordnilap
294	Divisors
325	Identifying legal pascal real constants
336	A node too far
343	What base is this
355	The bases are loaded
374	Big mod
389	Basically speaking
401	Palindromes
417	Word index
424	Integer inquiry
444	Encoder and decoder
446	Kibbles n bits n bits n bits
458	The decoder
459	Graph connectivity
465	Overflow
482	Permutation arrays
483	Word scramble
490	Rotating sentences
492	Pig latin
494	Kindergarten counting game
499	What's the frequency, kenneth
532	Dungeon master
543	Goldbach's conjecture
572	Oil deposits
573	The snail
591	Box of bricks
621	Secret research
623	500!
661	Blowing fuses
686	Goldbach's conjecture (ii)
713	Adding reversed numbers
725	Division
784	Maze exploration
785	Grid colouring
793	Network connections
865	Substitution cypher
902	Password search
978	Lemmings battle!
1124	Celebrity jeopardy
1197	The suspects
1225	Digit counting
1230	Modex
10004	Bicoloring
10008	What's cryptanalysis
10018	Reverse and add
10019	Funny encryption method
10034	Freckles
10035	Primary arithmetic
10038	Jolly jumpers
10062	Tell me the frequencies!
10070	Leap year or not leap year
10114	Loansome car buyer
10140	Prime distance
10220	I love big numbers!
10222	Decode the mad man
10235	Simply emirp
10252	Common permutation
10260	Soundex
10281	Average speed
10293	Word length and frequency
10324	Zeros and ones
10338	Mischievous children
10346	Peter's smokes
10370	Above average
10374	Election
10393	The one handed typist
10420	List of conquests
10424	Love calculator
10473	Simple base conversion
10474	Where is the marble
10523	Very easy
10524	Matrix reloaded
10551	Basic remains
10583	Ubiquitous religions
10591	Happy number
10608	Friends
10611	The playboy chimp
10685	Nature
10789	Prime frequency
10815	Andy's first dictionary
10878	Decode the tape
10892	Lcm cardinality
10919	Prerequisites
10921	Find the telephone
10929	You can say 11
10945	Mother bear
10963	The swallowing ground
11044	Searching for nessy
11059	Maximum product
11062	Andy's second dictionary
11080	Place the guards
11136	Hoax or what
11185	Ternary
11192	Group reverse
11220	Decoding the message
11278	One handed typist
11332	Summing digits
11340	Newspaper
11364	Parking
11388	Gcd lcm
11396	Claw decomposition
11417	Gcd
11462	Age sort
11498	Division of nlogonia
11530	Sms typing
11541	Decoding
11559	Event planning
11577	Letter frequency
11586	Train tracks
11608	No problem!
11631	Dark roads
11650	Mirror clock
11661	Burger time
11677	Alarm clock
11679	Sub prime
11710	Expensive subway
11713	Abstract names
11715	Car
11716	Digital fortress
11723	Numbering roads
11747	Heavy cycle edges
11764	Jumping mario
11799	Horror dash
11805	Bafana bafana
11827	Maximum gcd
11831	Sticker collector robot
11849	Cd
11850	Alaska
11875	Brick game
11877	The coco cola store
11879	Multiple of 11
11879	Multiple of 17
11942	Lumberjack sequencing
11946	Code number
11952	Arithmetic
11965	Extra spaces
12015	Google is feeling lucky
12049	Just prune the list
12136	Schedule of a married man
12149	Feynman
12279	Emoogle balance
12342	Tax calculator
12468	Zapping
12478	Hardest problem ever (easy)
12502	Three families
12503	Robot instructions
12527	Different digits
12554	A special happy birthday song!!!

Codeforces

Solved problems from Codeforces using Java. All the codes are tested in online-judge.

#	Title	Tag
1081A	Definite Game	Math
1084A	The Fair Nut and Elevator	Brute Force
1084B	Kvass and the Fair Nut	Greedy
1087A	Right-Left Cipher	String
1088A	Ehab and another construction problem	Brute Force, Constructive
1088B	Ehab and subtraction	Sorting
1092A	Uniform String	String
1092B	Teams Forming	Sorting
1093A	Dice Rolling	Math
1093B	Letters Rearranging	Greedy, Sortings
1097A	Gennady and a Card Game	Brute Force
1097B	Petr and a Combination Lock	Bitmasks, Brute Force
1099A	Snowball	Brute Force
1102A	Integer Sequence Dividing	Math