260 lines
8.6 KiB
YAML
260 lines
8.6 KiB
YAML
patterns:
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- name: Two Pointers
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slug: two-pointers
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description: Use two pointers to traverse data from different positions, often moving toward or away from each other.
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when_to_use: |
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- Sorted arrays where you need to find pairs
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- Linked list cycle detection
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- Removing duplicates in-place
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- Partitioning arrays
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- Palindrome checking
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- name: Sliding Window
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slug: sliding-window
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description: Maintain a window of elements that slides through the data, tracking a constraint or computing aggregates.
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when_to_use: |
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- Finding subarrays/substrings with specific properties
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- Maximum/minimum sum of fixed-size windows
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- Longest substring with at most K distinct characters
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- Problems mentioning "contiguous" elements
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- name: Fast & Slow Pointers
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slug: fast-slow-pointers
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description: Two pointers moving at different speeds, commonly used for cycle detection.
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when_to_use: |
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- Detecting cycles in linked lists or arrays
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- Finding the middle of a linked list
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- Finding the start of a cycle
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- Happy number problem
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- name: Binary Search
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slug: binary-search
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description: Efficiently search sorted data by repeatedly dividing the search space in half.
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when_to_use: |
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- Sorted arrays or search spaces
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- Finding boundaries (first/last occurrence)
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- Searching in rotated sorted arrays
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- Finding peak elements
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- Minimizing/maximizing with monotonic constraints
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- name: BFS (Breadth-First Search)
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slug: bfs
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description: Level-by-level traversal using a queue, optimal for shortest paths in unweighted graphs.
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when_to_use: |
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- Shortest path in unweighted graphs
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- Level-order tree traversal
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- Finding all nodes at distance K
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- Word ladder problems
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- Matrix traversal
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- name: DFS (Depth-First Search)
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slug: dfs
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description: Explore as deep as possible before backtracking, using recursion or a stack.
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when_to_use: |
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- Tree/graph traversal
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- Path finding
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- Detecting cycles
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- Topological sorting
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- Connected components
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- Backtracking problems
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- name: Backtracking
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slug: backtracking
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description: Build solutions incrementally, abandoning paths that fail to satisfy constraints.
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when_to_use: |
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- Generating all permutations/combinations
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- Sudoku solver
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- N-Queens problem
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- Subset/partition problems
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- Word search in grid
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- name: Dynamic Programming
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slug: dynamic-programming
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description: Break problems into overlapping subproblems, storing results to avoid recomputation.
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when_to_use: |
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- Optimization problems (min/max)
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- Counting problems
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- Problems with optimal substructure
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- Sequence alignment
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- Knapsack-type problems
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- name: Greedy
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slug: greedy
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description: Make locally optimal choices at each step, hoping for a global optimum.
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when_to_use: |
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- Interval scheduling
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- Huffman coding
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- Minimum spanning tree
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- Activity selection
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- When local optimum leads to global optimum
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- name: Monotonic Stack
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slug: monotonic-stack
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description: Stack maintaining elements in sorted order, used for next greater/smaller element problems.
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when_to_use: |
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- Next greater/smaller element
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- Largest rectangle in histogram
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- Daily temperatures
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- Stock span problem
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- Trapping rain water
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- name: Heap / Priority Queue
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slug: heap
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description: Data structure for efficiently finding min/max elements.
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when_to_use: |
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- Top K elements
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- K-way merge
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- Median from data stream
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- Task scheduling
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- Dijkstra's algorithm
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- name: Union Find
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slug: union-find
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description: Track disjoint sets with efficient union and find operations.
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when_to_use: |
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- Connected components in graphs
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- Cycle detection in undirected graphs
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- Kruskal's minimum spanning tree
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- Social network connections
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- Accounts merge
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- name: Trie
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slug: trie
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description: Tree-like data structure for efficient string prefix operations.
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when_to_use: |
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- Autocomplete systems
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- Word dictionary with wildcard search
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- Longest common prefix
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- Word break problems
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- Spell checker
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- name: Prefix Sum
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slug: prefix-sum
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description: Precompute cumulative sums to answer range queries in O(1) time.
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when_to_use: |
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- Range sum queries
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- Subarray sum equals target
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- Product of array except self
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- Count subarrays with given sum
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- 2D matrix region sums
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- name: LinkedList In-Place Reversal
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slug: linkedlist-reversal
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description: Reverse linked list nodes in-place by manipulating pointers without extra space.
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when_to_use: |
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- Reverse entire linked list
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- Reverse a portion of linked list
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- Reverse in groups of K
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- Palindrome linked list check
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- Reorder list problems
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- name: Overlapping Intervals
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slug: intervals
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description: Process and merge intervals that share common ranges.
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when_to_use: |
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- Merge overlapping intervals
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- Insert interval into sorted list
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- Meeting rooms scheduling
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- Find gaps between intervals
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- Interval intersection problems
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- name: Binary Tree Traversal
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slug: tree-traversal
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description: Visit tree nodes in specific orders - preorder, inorder, postorder, or level-order.
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when_to_use: |
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- Serialize/deserialize trees
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- Validate BST (inorder)
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- Copy or compare trees
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- Path sum problems
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- Tree construction from traversals
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- name: Matrix Traversal
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slug: matrix-traversal
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description: Navigate 2D grids using DFS, BFS, or directional iteration.
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when_to_use: |
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- Number of islands / connected regions
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- Shortest path in grid
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- Flood fill
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- Rotting oranges
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- Word search in grid
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- name: Topological Sort
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slug: topological-sort
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description: Order vertices in a directed acyclic graph (DAG) such that for every edge u→v, u comes before v.
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when_to_use: |
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- Course scheduling with prerequisites
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- Build order / dependency resolution
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- Task scheduling with dependencies
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- Alien dictionary problems
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- Detecting cycles in directed graphs
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- name: Bit Manipulation
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slug: bit-manipulation
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description: Use bitwise operations (AND, OR, XOR, shifts) to solve problems efficiently.
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when_to_use: |
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- Finding single/missing numbers (XOR tricks)
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- Counting set bits
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- Power of two checks
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- Subset generation with bitmasks
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- Swapping without temp variable
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- name: Counting / Bucket Sort
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slug: counting-sort
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description: Sort or process elements by using their values as indices when the range is bounded.
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when_to_use: |
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- Top K frequent elements (bounded frequency range)
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- Sort Colors (Dutch National Flag)
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- H-Index calculation
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- Problems where values are in known small range
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- Frequency-based grouping
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- name: Cyclic Sort
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slug: cyclic-sort
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description: Place each element at its correct index when values are in range [1, n] or [0, n-1].
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when_to_use: |
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- Find missing number in [1, n]
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- Find duplicate in [1, n]
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- Find all missing/duplicate numbers
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- First missing positive
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- Set mismatch problems
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- name: Divide and Conquer
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slug: divide-and-conquer
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description: Split problem into smaller subproblems, solve recursively, and combine results.
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when_to_use: |
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- Merge sort and related problems
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- Quick select for kth element
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- Binary search variants
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- Matrix multiplication
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- Closest pair of points
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- name: Hashing
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slug: hashing
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description: Use hash tables for O(1) average lookup, insertion, and deletion.
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when_to_use: |
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- Two Sum and variants
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- Detecting duplicates
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- Frequency counting
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- Anagram grouping
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- LRU/LFU cache implementation
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- name: Matrix Manipulation
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slug: matrix-manipulation
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description: Transform or process 2D matrices using rotation, transposition, or in-place modifications.
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when_to_use: |
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- Rotate image 90 degrees
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- Spiral matrix traversal
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- Set matrix zeroes
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- Transpose matrix
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- Game of Life state updates
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- name: Synchronization
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slug: synchronization
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description: Coordinate multiple threads or processes using locks, semaphores, or barriers.
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when_to_use: |
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- Print in order problems
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- Producer-consumer patterns
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- Dining philosophers
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- Building H2O molecules
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- Concurrent data structure design
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