Rulcode.com is an open-source platform to learn, visualize, and master algorithms with interactive explanations and multi-language code snippets (Python, Java, C++, and TypeScript).
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Arrays & Strings
- Two Pointers — Use two pointers to traverse arrays efficiently
- Sliding Window — Maintain a window of elements for efficient computation
- Prefix Sum — Pre-compute cumulative sums for range queries
- Binary Search — Search in sorted arrays in logarithmic time
- Kadane's Algorithm — Find maximum subarray sum efficiently
- Dutch National Flag — Sort array of three distinct elements
- Merge Intervals — Merge overlapping intervals
- Monotonic Stack — Stack with monotonic properties for efficient queries
- Rotate Array In-Place — Rotate array elements without extra space
- Cyclic Sort — Sort by placing elements at their correct index
Linked List
- Fast & Slow Pointers — Detect cycles and find middle using two pointers
- Reverse Linked List — Reverse a singly linked list
- Merge Two Sorted Lists — Merge two sorted linked lists
- Detect Cycle — Floyd's algorithm to detect cycles
- Middle Node — Find middle node using fast and slow pointers
Trees & BSTs
- DFS Preorder — Visit root, left, then right subtree
- DFS Inorder — Visit left, root, then right subtree
- DFS Postorder — Visit left, right, then root
- BFS Level Order — Traverse tree level by level
- BST Insert — Insert node in binary search tree
- Lowest Common Ancestor — Find LCA of two nodes in tree
- Recover BST — Fix BST with two swapped nodes
- Serialize Tree — Serialize and deserialize binary tree
- Trie (Prefix Tree) — Efficient string storage and retrieval
Graphs
- Graph DFS — Depth-first traversal of graphs
- Graph BFS — Breadth-first traversal of graphs
- Topological Sort — Kahn's algorithm for DAG ordering
- Union-Find — Disjoint set data structure
- Kruskal's Algorithm — Find minimum spanning tree
- Prim's Algorithm — Find MST using greedy approach
- Dijkstra's Algorithm — Single-source shortest path
- Bellman-Ford — Shortest path with negative weights
- Floyd-Warshall — All-pairs shortest paths
- A* Search — Heuristic pathfinding algorithm
Dynamic Programming
- 0/1 Knapsack — Maximize value with weight constraint
- Coin Change — Minimum coins for target amount
- Longest Common Subsequence — Find longest common subsequence
- Longest Increasing Subsequence — Find LIS in array
- Edit Distance — Minimum edits to transform strings
- Matrix Path DP — Find unique or minimum paths in matrix
- Partition Equal Subset — Check if array can be partitioned equally
- House Robber — Maximum sum without adjacent elements
- Climbing Stairs — Count ways to climb n stairs
- Word Break — Segment string into dictionary words
Greedy
- Activity Selection — Select maximum non-overlapping activities
- Interval Scheduling — Schedule intervals optimally
- Huffman Encoding — Optimal prefix-free encoding
- Gas Station — Find starting station for circular tour
Backtracking
- Subsets — Generate all subsets of a set
- Permutations — Generate all permutations
- Combinations — Generate all k-combinations
- Combination Sum — Find combinations summing to target
- Word Search — Find word in 2D grid
- N-Queens — Place N queens on N×N board
- Sudoku Solver — Solve Sudoku puzzle
Bit Manipulation
- XOR Trick — Find single number using XOR
- Count Bits — Brian Kernighan's algorithm
- Subset Generation with Bits — Generate subsets using bitmasks
Heap / Priority Queue
- Kth Largest Element — Find kth largest using min heap
- Merge K Sorted Lists — Merge using min heap
- Sliding Window Maximum — Find max in each window
Math & Number Theory
- GCD (Euclidean) — Euclid's algorithm for GCD
- Sieve of Eratosthenes — Generate all primes up to n
- Modular Exponentiation — Fast power with modulo
- Karatsuba Multiplication — Fast multiplication algorithm
Advanced
- Segment Tree — Range query data structure
- Fenwick Tree (BIT) — Binary indexed tree for prefix sums
- Sparse Table — Range minimum query in O(1)
- KMP String Matching — Linear time pattern matching
- Rabin-Karp — Rolling hash pattern matching
- Manacher's Algorithm — Longest palindromic substring
- Union by Rank + Path Compression — Optimized union-find
- Tarjan's Algorithm — Find strongly connected components
- Binary Lifting — LCA using binary lifting
// ...existing code...
Blind 75 Problems
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Array & Hashing
- Two Sum — Find pair that sums to target
- Contains Duplicate — Check for duplicates in array
- Valid Anagram — Check if strings are anagrams
- Group Anagrams — Group strings by anagram
- Top K Frequent — Find k most frequent elements
- Product Except Self — Array product without division
- Encode Decode Strings — Encode/decode string array
- Longest Consecutive — Longest consecutive sequence
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Two Pointers
- Valid Palindrome — Check if string is palindrome
- Three Sum — Find triplets that sum to zero
- Container With Most Water — Max water container area
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Sliding Window
- Best Time to Buy Sell — Max profit from stock prices
- Longest Substring — Longest substring without repeating chars
- Longest Repeating — Longest repeating char replacement
- Minimum Window — Minimum window substring
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Stack
- Valid Parentheses — Check valid bracket sequence
- Min Stack — Stack with constant time minimum
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Binary Search
- Find Minimum in Rotated — Min in rotated sorted array
- Search in Rotated — Search in rotated sorted array
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Trees
- Maximum Depth — Max depth of binary tree
- Same Tree — Check if trees are identical
- Invert Binary Tree — Mirror a binary tree
- Binary Tree Maximum Path — Max path sum in binary tree
- Binary Tree Level Order — Level order traversal
- Serialize Deserialize — Serialize/deserialize binary tree
- Subtree of Another — Check if tree is subtree
- Construct from Preorder — Build tree from traversal
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Tries
- Implement Trie — Implement prefix tree
- Word Search II — Find words in board using trie
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Heap / Priority Queue
- Find Median from Stream — Running median with heaps
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Backtracking
- Combination Sum — Find combinations that sum to target
- Word Search — Find word in board
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Graphs
- Number of Islands — Count islands in grid
- Clone Graph — Deep copy of graph
- Pacific Atlantic — Water flow between oceans
- Course Schedule — Course prerequisites graph
- Number of Connected — Count connected components
- Graph Valid Tree — Check if graph is valid tree
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Dynamic Programming
- Climbing Stairs — Ways to climb n stairs
- House Robber — Max money without adjacent houses
- House Robber II — Circular house robber
- Longest Palindromic — Longest palindromic substring
- Unique Paths — Unique paths in grid
- Jump Game — Can reach last index
// ...existing code...
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