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class Solution {
      public int[] twoSum(int[] nums, int target) {
          Map<Integer, Integer> map = new HashMap<>();
          
          for (int i = 0; i < nums.length; i++) {
              int complement = target - nums[i];
              if (map.containsKey(complement)) {
                  return new int[] { map.get(complement), i };
              }
              map.put(nums[i], i);
          }
          return null;
      }
  }

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424+ Problems

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Comprehensive coverage of all important DSA topics

Beginner Problems

83 Problems

Easy: 64 Medium: 3 Hard: 0

0/83 - 0% Completed

Sorting

5 Problems

Easy: 4 Medium: 1 Hard: 0

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Arrays

28 Problems

Easy: 11 Medium: 10 Hard: 7

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Hashing

4 Problems

Easy: 0 Medium: 0 Hard: 4

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Binary Search

28 Problems

Easy: 10 Medium: 6 Hard: 12

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Recursion

17 Problems

Easy: 5 Medium: 5 Hard: 7

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Linked-List

44 Problems

Easy: 18 Medium: 12 Hard: 8

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Bit Manipulation

8 Problems

Easy: 0 Medium: 7 Hard: 0

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Greedy Algorithms

11 Problems

Easy: 3 Medium: 6 Hard: 2

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Sliding Window / 2 Pointer

11 Problems

Easy: 0 Medium: 1 Hard: 9

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Stack / Queues

23 Problems

Easy: 7 Medium: 6 Hard: 9

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Binary Trees

30 Problems

Easy: 5 Medium: 13 Hard: 11

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Binary Search Trees

14 Problems

Easy: 2 Medium: 7 Hard: 4

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Heaps

10 Problems

Easy: 0 Medium: 8 Hard: 1

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Graphs

44 Problems

Easy: 0 Medium: 10 Hard: 32

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Dynamic Programming

47 Problems

Easy: 6 Medium: 16 Hard: 24

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Tries

6 Problems

Easy: 0 Medium: 0 Hard: 6

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Strings (Advanced Algo)

8 Problems

Easy: 0 Medium: 0 Hard: 8

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Maths

3 Problems

Easy: 0 Medium: 0 Hard: 3

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Beginner Problems

No.	Subcategory	Problem	Link	Difficulty
1	Language Basics	CPP Setup	N/A
2	Language Basics	Cpp Basics	N/A
3	Language Basics	Java Setup	N/A
4	Language Basics	Java Basics	N/A
5	Language Basics	Java OOPs Basic	N/A
6	Language Basics	Input Output	N/A	Easy
7	Language Basics	If Else Adult Teen Problem	N/A	Easy
8	Language Basics	If ElseIf	N/A	Easy
9	Language Basics	Switch Case	N/A	Easy
10	Language Basics	Sum of first last element in array	N/A	Easy
11	Language Basics	Print X N numbers of times	N/A	Easy
12	Language Basics	Print last character of string	N/A	Easy
13	Logic Building (Patterns)	Easy and Medium	N/A
14	Logic Building (Patterns)	Hard	N/A
15	Patterns	Pattern 1	N/A	Easy
16	Patterns	Pattern 2	N/A	Easy
17	Patterns	Pattern 3	N/A	Easy
18	Patterns	Pattern 4	N/A	Easy
19	Patterns	Pattern 5	N/A	Easy
20	Patterns	Pattern 6	N/A	Easy
21	Patterns	Pattern 7	N/A	Easy
22	Patterns	Pattern 8	N/A	Easy
23	Patterns	Pattern 9	N/A	Easy
24	Patterns	Pattern 10	N/A	Easy
25	Patterns	Pattern 11	N/A	Easy
26	Patterns	Pattern 12	N/A	Easy
27	Patterns	Pattern 13	N/A	Easy
28	Patterns	Pattern 14	N/A	Easy
29	Patterns	Pattern 15	N/A	Easy
30	Patterns	Pattern 16	N/A	Easy
31	Patterns	Pattern 17	N/A	Easy
32	Patterns	Pattern 18	N/A	Easy
33	Patterns	Pattern 19	N/A	Easy
34	Patterns	Pattern 20	N/A	Medium
35	Patterns	Pattern 21	N/A	Medium
36	Patterns	Pattern 22	N/A	Medium
37	Time Complexity	Theory with examples	N/A
38	STL and Collections	STL	N/A
39	STL and Collections	Java Collections	N/A
40	Concept Basics	Basic Maths	N/A
41	Concept Basics	Basic Arrays	N/A
42	Concept Basics	Basic Hashing	N/A
43	Concept Basics	Basic String	N/A
44	Basic Maths	Count all digits of a number		Easy
45	Basic Maths	Count number of odd digits in a number		Easy
46	Basic Maths	Reverse a number		Easy
47	Basic Maths	Palindrome number		Easy
48	Basic Maths	Return the largest digit in a number		Easy
49	Basic Maths	Factorial of a given number		Easy
50	Basic Maths	Check if the number is armstrong		Easy
51	Basic Maths	Check for perfect number		Easy
52	Basic Maths	Check for prime number		Easy
53	Basic Maths	Count of prime numbers till N		Easy
54	Basic Maths	GCD of two numbers		Easy
55	Basic Maths	LCM of two numbers		Easy
56	Basic Maths	Divisors of a number		Easy
57	Basic Arrays	Sum of array elements		Easy
58	Basic Arrays	Count of odd numbers in array		Easy
59	Basic Arrays	Reverse an array		Easy
60	Basic Arrays	Check if the array is sorted		Easy
61	Basic Hashing	Highest occurring element in an array		Easy
62	Basic Hashing	Second highest occurring element		Easy
63	Basic Hashing	Sum of highest and lowest frequency		Easy
64	Basic Strings	Reverse a string		Easy
65	Basic Strings	Palindrome Check		Easy
66	Basic Strings	Largest odd number in a string		Easy
67	Basic Strings	Longest common prefix		Easy
68	Basic Strings	Isomorphic string		Easy
69	Basic Strings	Rotate string		Easy
70	Basic Strings	Valid Anagram		Easy
71	Basic Strings	Sort characters by frequency		Easy
72	Basic Recursion	Recursion Theory
73	Basic Recursion	Recursion Concepts with Parameters
74	Basic Recursion	Sum of first N numbers		Easy
75	Basic Recursion	Factorial of a given number		Easy
76	Basic Recursion	Sum of array elements		Easy
77	Basic Recursion	Reverse a string		Easy
78	Basic Recursion	Check if string is palindrome or not		Easy
79	Basic Recursion	Check if a number is prime or not		Easy
80	Basic Recursion	Reverse an array		Easy
81	Basic Recursion	Check if the array is sorted		Easy
82	Basic Recursion	Sum of digits in a given number		Easy
83	Basic Recursion	Fibonacci Number		Easy

No.	Subcategory	Problem	Difficulty
1	Algorithms	Selection Sort	Easy
2	Algorithms	Bubble Sort	Easy
3	Algorithms	Insertion Sorting	Easy
4	Algorithms	Merge Sorting	Medium
5	Algorithms	Quick Sorting	Easy

No.	Subcategory	Problem	Difficulty
1	Fundamentals	Linear Search	Easy
2	Fundamentals	Largest Element	Easy
3	Fundamentals	Second Largest Element	Easy
4	Fundamentals	Maximum Consecutive Ones	Easy
5	Fundamentals	Left Rotate Array by One	Easy
6	Fundamentals	Left Rotate Array by K Places	Easy
7	Logic Building	Move Zeros to End	Easy
8	Logic Building	Remove duplicates from sorted array	Easy
9	Logic Building	Find missing number	Easy
10	Logic Building	Union of two sorted arrays	Easy
11	Logic Building	Intersection of two sorted arrays	Easy
12	FAQs(Medium)	Leaders in an Array	Medium
13	FAQs(Medium)	Print the matrix in spiral manner	Medium
14	FAQs(Medium)	Rearrange array elements by sign	Medium
15	FAQs(Medium)	Pascal's Triangle	Medium
16	FAQs(Medium)	Rotate matrix by 90 degrees	Medium
17	FAQs(Medium)	Two Sum	Medium
18	FAQs(Medium)	3 Sum	Medium
19	FAQs(Medium)	4 Sum	Medium
20	FAQs(Medium)	Sort an array of 0's 1's and 2's	Medium
21	FAQs(Medium)	Kadane's Algorithm	Medium
22	FAQs(Hard)	Majority Element-I	Hard
23	FAQs(Hard)	Majority Element-II	Hard
24	FAQs(Hard)	Find the repeating and missing number	Hard
25	FAQs(Hard)	Count Inversions	Hard
26	FAQs(Hard)	Reverse Pairs	Hard
27	FAQs(Hard)	Maximum Product Subarray in an Array	Hard
28	FAQs(Hard)	Merge two sorted arrays without extra space	Hard

Hashing

No.	Subcategory	Problem	Difficulty
1	FAQs	Longest Consecutive Sequence in an Array	Hard
2	FAQs	Longest subarray with sum K	Hard
3	FAQs	Count subarrays with given sum	Hard
4	FAQs	Count subarrays with given xor K	Hard

Binary Search

No.	Subcategory	Problem	Difficulty
1	Fundamentals	Search X in sorted array	Easy
2	Fundamentals	Lower Bound	Easy
3	Fundamentals	Upper Bound	Easy
4	Logic Building	Search insert position	Easy
5	Logic Building	Floor and Ceil in Sorted Array	Easy
6	Logic Building	First and last occurrence	Easy
7	Logic Building	Search in rotated sorted array-I	Easy
8	Logic Building	Search in rotated sorted array-II	Easy
9	Logic Building	Find minimum in Rotated Sorted Array	Easy
10	Logic Building	Find out how many times the array is rotated	Easy
11	Logic Building	Single element in sorted array	Medium
12	On answers	Find square root of a number	Medium
13	On answers	Find Nth root of a number	Medium
14	On answers	Find the smallest divisor	Medium
15	On answers	Koko eating bananas	Medium
16	On answers	Minimum days to make M bouquets	Medium
17	FAQs	Aggressive Cows	Hard
18	FAQs	Book Allocation Problem	Hard
19	FAQs	Find peak element	Hard
20	FAQs	Median of 2 sorted arrays	Hard
21	FAQs	Minimise max distance to gas stations	Hard
22	FAQs	Kth element of 2 sorted arrays	Hard
23	FAQs	Split array - largest sum	Hard
24	2D Arrays	Find row with maximum 1's	Hard
25	2D Arrays	Search in a 2D matrix	Hard
26	2D Arrays	Search in 2D matrix - II	Hard
27	2D Arrays	Find Peak Element	Hard
28	2D Arrays	Matrix Median	Hard

Recursion

No.	Subcategory	Problem	Difficulty
1	Implementation Problems	Pow(x,n)	Easy
2	Implementation Problems	Generate Paranthesis	Easy
3	Implementation Problems	Power Set	Easy
4	Subsequence Pattern Problems	Check if there exists a subsequence with sum K	Easy
5	Subsequence Pattern Problems	Count all subsequences with sum K	Easy
6	FAQs (Medium)	Combination Sum	Medium
7	FAQs (Medium)	Combination Sum II	Medium
8	FAQs (Medium)	Subsets I	Medium
9	FAQs (Medium)	Subsets II	Medium
10	FAQs (Medium)	Combination Sum III	Medium
11	Hard	Letter Combinations of a Phone Number	Hard
12	FAQs (Hard)	Palindrome partitioning	Hard
13	FAQs (Hard)	Word Search	Hard
14	FAQs (Hard)	N Queen	Hard
15	FAQs (Hard)	Rat in a Maze	Hard
16	FAQs (Hard)	M Coloring Problem	Hard
17	FAQs (Hard)	Sudoko Solver	Hard

Linked-List

No.	Subcategory	Problem	Difficulty
1	Fundamentals (Single LL)	Introduction to Singly LinkedList
2	Fundamentals (Single LL)	Traversal in Linked List	Easy
3	Fundamentals (Single LL)	Deletion in Linked List
4	Fundamentals (Single LL)	Insertion in Linked List
5	Fundamentals (Single LL)	Deletion of the head of LL	Easy
6	Fundamentals (Single LL)	Deletion of the tail of LL	Easy
7	Fundamentals (Single LL)	Deletion of the Kth element of LL	Easy
8	Fundamentals (Single LL)	Delete the element with value X	Easy
9	Fundamentals (Single LL)	Insertion at the head of LL	Easy
10	Fundamentals (Single LL)	Insertion at the tail of LL	Easy
11	Fundamentals (Single LL)	Insertion at the Kth position of LL	Easy
12	Fundamentals (Single LL)	Insertion before the value X in LL	Easy
13	Fundamentals (Doubly LL)	Introduction to Doubly LL
14	Fundamentals (Doubly LL)	Deletion in Doubly LL
15	Fundamentals (Doubly LL)	Insertion in DLL
16	Fundamentals (Doubly LL)	Convert Array to DLL	Easy
17	Fundamentals (Doubly LL)	Delete head of DLL	Easy
18	Fundamentals (Doubly LL)	Delete Tail of DLL	Easy
19	Fundamentals (Doubly LL)	Delete Kth Element of DLL	Easy
20	Fundamentals (Doubly LL)	Removing given node in DLL	Easy
21	Fundamentals (Doubly LL)	Insert node before head in DLL	Easy
22	Fundamentals (Doubly LL)	Insert node before tail in DLL	Easy
23	Fundamentals (Doubly LL)	Insert node before (kth node) in DLL	Easy
24	Fundamentals (Doubly LL)	Insert before given node in DLL	Easy
25	Logic Building	Add two numbers in LL	Medium
26	Logic Building	Segregate odd and even nodes in LL	Medium
27	Logic Building	Sort a LL of 0's 1's and 2's	Medium
28	Logic Building	Remove Nth node from the back of the LL	Medium
29	Logic Building	Reverse a LL	Medium
30	FAQs (Medium)	Add one to a number represented by LL	Medium
31	FAQs (Medium)	Check if LL is palindrome or not	Medium
32	FAQs (Medium)	Find the intersection point of Y LL	Medium
33	FAQs (Medium)	Detect a loop in LL	Medium
34	FAQs (Medium)	Find the starting point in LL	Medium
35	FAQs (Medium)	Length of loop in LL	Medium
36	FAQs (Medium)	Delete the middle node in LL	Medium
37	FAQs (Hard)	Reverse LL in group of given size K	Hard
38	FAQs (Hard)	Rotate a LL	Hard
39	FAQs (Hard)	Merge two Sorted Lists	Hard
40	FAQs (Hard)	Flattening of LL	Hard
41	FAQs (Hard)	Sort LL	Hard
42	FAQs (Hard)	Clone a LL with random and next pointer	Hard
43	FAQS (DLL)	Delete all occurrences of a key in DLL	Hard
44	FAQS (DLL)	Remove duplicated from sorted DLL	Hard

Bit Manipulation

No.	Subcategory	Problem	Difficulty
1	Theory	Introduction to Bits and Tricks
2	Problems	Minimum Bit Flips to Convert Number	Medium
3	Problems	Single Number - I	Medium
4	Problems	Single Number - II	Medium
5	Problems	Single Number - III	Medium
6	Problems	Divide two numbers without multiplication and division	Medium
7	Problems	Power Set Bit Manipulation	Medium
8	Problems	XOR of numbers in a given range	Medium

No.	Subcategory	Problem	Difficulty
1	Easy	Assign Cookies	Easy
2	Easy	Lemonade Change	Easy
3	Easy	Jump Game - I	Easy
4	Scheduling and Interval Problems	Shortest Job First	Medium
5	Scheduling and Interval Problems	Job sequencing Problem	Medium
6	Scheduling and Interval Problems	N meetings in one room	Medium
7	Scheduling and Interval Problems	Non-overlapping Intervals	Medium
8	Scheduling and Interval Problems	Insert Interval	Medium
9	Scheduling and Interval Problems	Minimum number of platforms required for a railway	Medium
10	Hard	Valid Paranthesis Checker	Hard
11	Hard	Candy	Hard

Sliding Window / 2 Pointer

No.	Subcategory	Problem	Difficulty
1	Pattern and Template	Theory
2	Constant Window	Maximum Points You Can Obtain from Cards	Medium
3	Longest and Smallest Window Problems	Longest Substring Without Repeating Characters	Hard
4	Longest and Smallest Window Problems	Max Consecutive Ones III	Hard
5	Longest and Smallest Window Problems	Fruit Into Baskets	Hard
6	Longest and Smallest Window Problems	Longest Substring With At Most K Distinct Characters	Hard
7	Longest and Smallest Window Problems	Longest Repeating Character Replacement	Hard
8	Longest and Smallest Window Problems	Minimum Window Substring	Hard
9	Counting Subarrays / Substrings Problems	Number of Substrings Containing All Three Characters	Hard
10	Counting Subarrays / Substrings Problems	Binary Subarrays With Sum	Hard
11	Counting Subarrays / Substrings Problems	Count number of Nice subarrays	Hard

Stack / Queues

No.	Subcategory	Problem	Difficulty
1	Implementation	Implementation using different DS
2	Implementation	Implement Stack using Arrays	Easy
3	Implementation	Implement Queue using Arrays	Easy
4	Implementation	Implement Stack using Queue	Easy
5	Implementation	Implement Queue using Stack	Easy
6	Implementation	Implement stack using Linkedlist	Easy
7	Implementation	Implement queue using Linkedlist	Easy
8	Implementation	Balanced Paranthesis	Easy
9	Monotonic Stack	Next Greater Element	Medium
10	Monotonic Stack	Next Greater Element - 2	Medium
11	Monotonic Stack	Asteroid Collision	Medium
12	Monotonic Stack	Sum of Subarray Minimums	Medium
13	Monotonic Stack	Sum of Subarray Ranges	Medium
14	Monotonic Stack	Remove K Digits	Medium
15	FAQs	Implement Min Stack	Hard
16	FAQs	Sliding Window Maximum	Hard
17	FAQs	Trapping Rainwater	Hard
18	FAQs	Largest rectangle in a histogram	Hard
19	FAQs	Maximum Rectangles	Hard
20	FAQs	Stock span problem	Hard
21	FAQs	Celebrity Problem	Hard
22	FAQs	LRU Cache	Hard
23	FAQs	LFU Cache	Hard

Binary Trees

No.	Subcategory	Problem	Difficulty
1	Theory/Traversals	Introduction
2	Theory/Traversals	Preorder Traversal	Easy
3	Theory/Traversals	Inorder Traversal	Easy
4	Theory/Traversals	Postorder Traversal	Easy
5	Theory/Traversals	Level Order Traversal	Easy
6	Theory/Traversals	Pre, Post, Inorder in one traversal	Easy
7	Medium Problems	Maximum Depth in BT	Medium
8	Medium Problems	Check if two trees are identical or not	Medium
9	Medium Problems	Check for balanced binary tree	Medium
10	Medium Problems	Diameter of Binary Tree	Medium
11	Medium Problems	Maximum path sum	Medium
12	Medium Problems	Check for symmetrical BTs	Medium
13	FAQs	Zig Zag or Spiral Traversal	Medium
14	FAQs	Boundary Traversal	Medium
15	FAQs	Vertical Order Traversal	Medium
16	FAQs	Top View of BT	Medium
17	FAQs	Bottom view of BT	Medium
18	FAQs	Right/Left View of BT	Medium
19	FAQs	Print root to node path in BT	Hard
20	FAQs	LCA in BT	Hard
21	FAQs	Maximum Width of BT	Medium
22	FAQs	Print all nodes at a distance of K in BT	Hard
23	FAQs	Minimum time taken to burn the BT from a given Node	Hard
24	FAQs	Count total nodes in a complete BT	Hard
25	Construction Problems	Requirements needed to construct a unique BT	Hard
26	Construction Problems	Construct a BT from Preorder and Inorder	Hard
27	Construction Problems	Construct a BT from Postorder and Inorder	Hard
28	Construction Problems	Serialize and De-serialize BT	Hard
29	Traversal in Constant Space	Morris Inorder Traversal	Hard
30	Traversal in Constant Space	Morris Preorder Traversal	Hard

Binary Search Trees

No.	Subcategory	Problem	Difficulty
1	Theory and Basics	Introduction to BST
2	Theory and Basics	Search in BST	Easy
3	Theory and Basics	Floor and Ceil in a BST	Easy
4	Medium	Insert a given node in BST	Medium
5	Medium	Delete a node in BST	Medium
6	Medium	Kth Smallest and Largest element in BST	Medium
7	Medium	Check if a tree is a BST or not	Medium
8	Medium	LCA in BST	Medium
9	Medium	Construct a BST from a preorder traversal	Medium
10	Medium	Inorder successor and predecessor in BST	Medium
11	FAQs	BST iterator	Hard
12	FAQs	Two sum in BST	Hard
13	FAQs	Correct BST with two nodes swapped	Hard
14	FAQs	Largest BST in Binary Tree	Hard

Heaps

No.	Subcategory	Problem	Difficulty
1	Theory and Implementation	Heaps (Theory Video)
2	Theory and Implementation	Heapify Algorithm	Medium
3	Theory and Implementation	Build heap from a given Array	Medium
4	Theory and Implementation	Implement Min Heap	Medium
5	Theory and Implementation	Implement Max Heap	Medium
6	Theory and Implementation	Check if an array represents a min heap	Medium
7	Theory and Implementation	Convert Min Heap to Max Heap	Medium
8	Theory and Implementation	Heap Sort	Medium
9	Theory and Implementation	K-th Largest element in an array	Medium
10	FAQs	Kth largest element in a stream of running integers	Hard

Graphs

No.	Subcategory	Problem	Difficulty
1	Theory and traversals	Introduction to Graph
2	Theory and traversals	Connected Components	Medium
3	Theory and traversals	Traversal Techniques	Medium
4	Traversal Problems	Number of provinces	Medium
5	Traversal Problems	Number of islands	Medium
6	Traversal Problems	Flood fill algorithm	Medium
7	Traversal Problems	Number of enclaves	Medium
8	Traversal Problems	Rotten Oranges	Medium
9	Traversal Problems	Distance of nearest cell having one	Medium
10	Traversal Problems	Surrounded Regions	Medium
11	Traversal Problems	Number of distinct islands	Medium
12	Cycles	Detect a cycle in an undirected graph	Hard
13	Cycles	Bipartite graph	Hard
14	Cycles	Topological sort or Kahn's algorithm	Hard
15	Cycles	Detect a cycle in a directed graph	Hard
16	Hard Problems	Find eventual safe states	Hard
17	Hard Problems	Course Schedule I	Hard
18	Hard Problems	Course Schedule II	Hard
19	Hard Problems	Alien Dictionary	Hard
20	Hard Problems	Shortest path in DAG	Hard
21	Hard Problems	Shortest path in undirected graph with unit weights	Hard
22	Hard Problems	Word ladder I	Hard
23	Hard Problems	Word ladder II	Hard
24	Shortest Path Algorithms	Dijkstra's algorithm	Hard
25	Shortest Path Algorithms	Print Shortest Path	Hard
26	Shortest Path Algorithms	Shortest Distance in a Binary Maze	Hard
27	Shortest Path Algorithms	Path with minimum effort	Hard
28	Shortest Path Algorithms	Cheapest flight within K stops	Hard
29	Shortest Path Algorithms	Minimum multiplications to reach end	Hard
30	Shortest Path Algorithms	Number of ways to arrive at destination	Hard
31	Shortest Path Algorithms	Bellman ford algorithm	Hard
32	Shortest Path Algorithms	Floyd warshall algorithm	Hard
33	Shortest Path Algorithms	Find the city with the smallest number of neighbors	Hard
34	Minimum Spanning Tree	MST theory
35	Minimum Spanning Tree	Disjoint Set	Hard
36	Minimum Spanning Tree	Find the MST weight	Hard
37	Hard Problems II	Number of operations to make network connected	Hard
38	Hard Problems II	Accounts merge	Hard
39	Hard Problems II	Number of islands II	Hard
40	Hard Problems II	Making a large island	Hard
41	Hard Problems II	Most stones removed with same row or column	Hard
42	Additional Algorithms	Kosaraju's algorithm	Hard
43	Additional Algorithms	Bridges in graph	Hard
44	Additional Algorithms	Articulation point in graph	Hard

No.	Subcategory	Problem	Difficulty
1	Introduction	Introduction to DP
2	1D DP	Climbing stairs	Medium
3	1D DP	Frog Jump	Medium
4	1D DP	Frog jump with K distances	Medium
5	1D DP	Maximum sum of non adjacent elements	Medium
6	1D DP	House robber	Medium
7	2D DP	Ninja's training	Medium
8	DP on grids	Grid unique paths	Medium
9	DP on grids	Unique paths II	Medium
10	DP on grids	Minimum path sum in grid	Medium
11	DP on grids	Triangle	Medium
12	DP on grids	Cherry pickup II	Medium
13	DP on stocks	Best time to buy and sell stock	Medium
14	DP on stocks	Best time to buy and sell stock II	Medium
15	DP on stocks	Best time to buy and sell stock III	Medium
16	DP on stocks	Best time to buy and sell stock IV	Medium
17	DP on stocks	Best time to buy and sell stock with transaction fees	Medium
18	DP on subsequences	Subset sum equals to target	Hard
19	DP on subsequences	Partition equal subset sum	Hard
20	DP on subsequences	Partition a set into two subsets with minimum absolute sum difference	Hard
21	DP on subsequences	Count subsets with sum K	Hard
22	DP on subsequences	Count partitions with given difference	Hard
23	DP on subsequences	0 and 1 Knapsack	Hard
24	DP on subsequences	Minimum coins	Hard
25	DP on subsequences	Target sum	Hard
26	DP on subsequences	Coin change II	Hard
27	DP on subsequences	Unbounded knapsack	Hard
28	DP on subsequences	Rod cutting problem	Hard
29	LIS	Longest Increasing Subsequence	Easy
30	LIS	Print Longest Increasing Subsequence	Easy
31	LIS	Largest Divisible Subset	Easy
32	LIS	Longest String Chain	Easy
33	LIS	Longest Bitonic Subsequence	Easy
34	LIS	Number of Longest Increasing Subsequences	Easy
35	DP on strings	Longest common subsequence	Hard
36	DP on strings	Longest common substring	Hard
37	DP on strings	Longest palindromic subsequence	Hard
38	DP on strings	Minimum insertions to make string palindrome	Hard
39	DP on strings	Minimum insertions or deletions to convert string A to B	Hard
40	DP on strings	Shortest common supersequence	Hard
41	DP on strings	Distinct subsequences	Hard
42	DP on strings	Edit distance	Hard
43	DP on strings	Wildcard matching	Hard
44	MCM DP	Matrix chain multiplication	Hard
45	MCM DP	Minimum cost to cut the stick	Hard
46	MCM DP	Burst balloons	Hard
47	MCM DP	Palindrome partitioning II	Hard

Tries

No.	Subcategory	Problem	Difficulty
1	Theory	Trie Implementation and Operations	Hard
2	Theory	Trie Implementation and Advanced Operations	Hard
3	Problems	Longest word with all prefixes	Hard
4	Problems	Number of distinct substrings in a string	Hard
5	Problems	Maximum XOR of two numbers in an array	Hard
6	Problems	Maximum Xor with an element from an array	Hard

Strings (Advanced Algo)

No.	Subcategory	Problem	Difficulty
1	Medium Problems	Reverse every word in a string	Hard
2	Medium Problems	Minimum number of bracket reversals to make an expression balanced	Hard
3	Medium Problems	Count and say	Hard
4	Advanced Problems (Less asked)	Rabin Karp Algorithm	Hard
5	Advanced Problems (Less asked)	Z function	Hard
6	Advanced Problems (Less asked)	KMP Algorithm or LPS array	Hard
7	Advanced Problems (Less asked)	Shortest Palindrome	Hard
8	Advanced Problems (Less asked)	Longest happy prefix	Hard

Maths

No.	Subcategory	Problem	Difficulty
1	Sieve of Eratosthenes	Print all primes till N	Hard
2	Sieve of Eratosthenes	Prime factorisation of a Number	Hard
3	Sieve of Eratosthenes	Count primes in range L to R	Hard

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