codetutor/backend/data/patterns/patterns.yaml

patterns:
  - name: Two Pointers
    slug: two-pointers
    description: Use two pointers to traverse data from different positions, often moving toward or away from each other.
    when_to_use: |
      - Sorted arrays where you need to find pairs
      - Linked list cycle detection
      - Removing duplicates in-place
      - Partitioning arrays
      - Palindrome checking

  - name: Sliding Window
    slug: sliding-window
    description: Maintain a window of elements that slides through the data, tracking a constraint or computing aggregates.
    when_to_use: |
      - Finding subarrays/substrings with specific properties
      - Maximum/minimum sum of fixed-size windows
      - Longest substring with at most K distinct characters
      - Problems mentioning "contiguous" elements

  - name: Fast & Slow Pointers
    slug: fast-slow-pointers
    description: Two pointers moving at different speeds, commonly used for cycle detection.
    when_to_use: |
      - Detecting cycles in linked lists or arrays
      - Finding the middle of a linked list
      - Finding the start of a cycle
      - Happy number problem

  - name: Binary Search
    slug: binary-search
    description: Efficiently search sorted data by repeatedly dividing the search space in half.
    when_to_use: |
      - Sorted arrays or search spaces
      - Finding boundaries (first/last occurrence)
      - Searching in rotated sorted arrays
      - Finding peak elements
      - Minimizing/maximizing with monotonic constraints

  - name: BFS (Breadth-First Search)
    slug: bfs
    description: Level-by-level traversal using a queue, optimal for shortest paths in unweighted graphs.
    when_to_use: |
      - Shortest path in unweighted graphs
      - Level-order tree traversal
      - Finding all nodes at distance K
      - Word ladder problems
      - Matrix traversal

  - name: DFS (Depth-First Search)
    slug: dfs
    description: Explore as deep as possible before backtracking, using recursion or a stack.
    when_to_use: |
      - Tree/graph traversal
      - Path finding
      - Detecting cycles
      - Topological sorting
      - Connected components
      - Backtracking problems

  - name: Backtracking
    slug: backtracking
    description: Build solutions incrementally, abandoning paths that fail to satisfy constraints.
    when_to_use: |
      - Generating all permutations/combinations
      - Sudoku solver
      - N-Queens problem
      - Subset/partition problems
      - Word search in grid

  - name: Dynamic Programming
    slug: dynamic-programming
    description: Break problems into overlapping subproblems, storing results to avoid recomputation.
    when_to_use: |
      - Optimization problems (min/max)
      - Counting problems
      - Problems with optimal substructure
      - Sequence alignment
      - Knapsack-type problems

  - name: Greedy
    slug: greedy
    description: Make locally optimal choices at each step, hoping for a global optimum.
    when_to_use: |
      - Interval scheduling
      - Huffman coding
      - Minimum spanning tree
      - Activity selection
      - When local optimum leads to global optimum

  - name: Monotonic Stack
    slug: monotonic-stack
    description: Stack maintaining elements in sorted order, used for next greater/smaller element problems.
    when_to_use: |
      - Next greater/smaller element
      - Largest rectangle in histogram
      - Daily temperatures
      - Stock span problem
      - Trapping rain water

  - name: Heap / Priority Queue
    slug: heap
    description: Data structure for efficiently finding min/max elements.
    when_to_use: |
      - Top K elements
      - K-way merge
      - Median from data stream
      - Task scheduling
      - Dijkstra's algorithm

  - name: Union Find
    slug: union-find
    description: Track disjoint sets with efficient union and find operations.
    when_to_use: |
      - Connected components in graphs
      - Cycle detection in undirected graphs
      - Kruskal's minimum spanning tree
      - Social network connections
      - Accounts merge

  - name: Trie
    slug: trie
    description: Tree-like data structure for efficient string prefix operations.
    when_to_use: |
      - Autocomplete systems
      - Word dictionary with wildcard search
      - Longest common prefix
      - Word break problems
      - Spell checker

  - name: Prefix Sum
    slug: prefix-sum
    description: Precompute cumulative sums to answer range queries in O(1) time.
    when_to_use: |
      - Range sum queries
      - Subarray sum equals target
      - Product of array except self
      - Count subarrays with given sum
      - 2D matrix region sums

  - name: LinkedList In-Place Reversal
    slug: linkedlist-reversal
    description: Reverse linked list nodes in-place by manipulating pointers without extra space.
    when_to_use: |
      - Reverse entire linked list
      - Reverse a portion of linked list
      - Reverse in groups of K
      - Palindrome linked list check
      - Reorder list problems

  - name: Overlapping Intervals
    slug: intervals
    description: Process and merge intervals that share common ranges.
    when_to_use: |
      - Merge overlapping intervals
      - Insert interval into sorted list
      - Meeting rooms scheduling
      - Find gaps between intervals
      - Interval intersection problems

  - name: Binary Tree Traversal
    slug: tree-traversal
    description: Visit tree nodes in specific orders - preorder, inorder, postorder, or level-order.
    when_to_use: |
      - Serialize/deserialize trees
      - Validate BST (inorder)
      - Copy or compare trees
      - Path sum problems
      - Tree construction from traversals

  - name: Matrix Traversal
    slug: matrix-traversal
    description: Navigate 2D grids using DFS, BFS, or directional iteration.
    when_to_use: |
      - Number of islands / connected regions
      - Shortest path in grid
      - Flood fill
      - Rotting oranges
      - Word search in grid