When to Use What -- Decision Tree

graph TD
    START["What does the problem ask for?"]

    START --> FIND["Find / search for something"]
    START --> OPTIMIZE["Optimize a value<br/>(min cost, max profit, count ways)"]
    START --> GENERATE["Generate all / enumerate"]
    START --> SEQUENCE["Process a sequence<br/>(subarray, substring)"]
    START --> GRAPH["Graph structure<br/>(explicit or implicit)"]
    START --> DESIGN["Design a data structure"]

    %% FIND branch
    FIND --> SORTED{"Input is sorted?"}
    SORTED -->|YES| BSEARCH["Binary Search<br/>searching/binary_search.py"]
    SORTED -->|"Rotated?"| ROTATED["search_rotated_array.py<br/>find_minimum_rotated.py"]
    SORTED -->|NO| HASHMAP["Hash Map O(n) lookup<br/>arrays/two_sum.py"]
    FIND --> FINDGRAPH{"Find in a graph?"}
    FINDGRAPH -->|Unweighted| BFS["BFS<br/>graphs/number_of_islands.py"]
    FINDGRAPH -->|"Weighted +"| DIJKSTRA["Dijkstra<br/>graphs/dijkstra.py"]
    FINDGRAPH -->|"Weighted -"| BELLMAN["Bellman-Ford<br/>graphs/bellman_ford.py"]
    FINDGRAPH -->|Heuristic| ASTAR["A* Search<br/>graphs/a_star_search.py"]

    %% OPTIMIZE branch
    OPTIMIZE --> OVERLAP{"Overlapping<br/>subproblems?"}
    OVERLAP -->|YES| DP["Dynamic Programming"]
    DP --> DP1D["1D: climbing_stairs, coin_change"]
    DP --> DP2D["2D: edit_distance, longest_common_subseq"]
    DP --> DPBIT["Bitmask: traveling_salesman_dp"]
    OVERLAP -->|NO| GREEDY["Greedy<br/>merge_intervals, jump_game,<br/>interval_scheduling"]
    OPTIMIZE --> TOPK{"Top-K or<br/>priority ordering?"}
    TOPK -->|"Kth element"| HEAP["Heap<br/>heaps/kth_largest.py"]
    TOPK -->|"Merge K"| HEAPMERGE["Heap Merge<br/>heaps/merge_k_sorted_lists.py"]

    %% GENERATE branch
    GENERATE --> SUBSETS["All subsets<br/>backtracking/subsets.py"]
    GENERATE --> PERMS["All permutations<br/>backtracking/permutations.py"]
    GENERATE --> COMBSUM["Combinations to sum<br/>backtracking/combination_sum.py"]
    GENERATE --> PLACEMENT["Placement with rules<br/>backtracking/n_queens.py"]

    %% SEQUENCE branch
    SEQUENCE --> CONTIG{"Contiguous?"}
    CONTIG -->|YES| WINDOW["Sliding Window"]
    WINDOW --> FIXEDWIN["Fixed size: standard pattern"]
    WINDOW --> VARWIN["Variable: min_window_substring,<br/>longest_substring_no_repeat"]
    CONTIG -->|NO| SUBSEQ["Subsequence DP<br/>longest_increasing_subseq,<br/>longest_common_subseq"]
    SEQUENCE --> NEXTGT["Next greater/smaller?<br/>Monotonic Stack<br/>stacks_queues/daily_temperatures.py"]
    SEQUENCE --> NESTING["Valid nesting?<br/>Stack<br/>stacks_queues/valid_parentheses.py"]

    %% GRAPH branch
    GRAPH --> COMPONENTS["Connected components<br/>DFS/BFS or Union-Find<br/>graphs/number_of_islands.py"]
    GRAPH --> DEPORDER["Dependency ordering<br/>Topological Sort<br/>graphs/topological_sort.py"]
    GRAPH --> CYCLE["Cycle detection<br/>graphs/course_schedule.py"]
    GRAPH --> CLONE["Clone / copy<br/>graphs/clone_graph.py"]
    GRAPH --> MST["Min spanning tree<br/>graphs/minimum_spanning_tree.py"]
    GRAPH --> MAXFLOW["Maximum flow<br/>graphs/network_flow.py"]

    %% DESIGN branch
    DESIGN --> LRU["O(1) access + eviction<br/>linked_lists/lru_cache.py"]
    DESIGN --> MINSTACK["O(1) min/max retrieval<br/>stacks_queues/min_stack.py"]
    DESIGN --> SORTEDDS["Sorted insert + search<br/>bisect / SortedList"]
    DESIGN --> GENERIC["Generic typed container<br/>concepts/advanced_typing.py"]

    %% Styling
    classDef start fill:#6366f1,color:#fff,stroke:#4f46e5
    classDef branch fill:#f59e0b,color:#000,stroke:#d97706
    classDef leaf fill:#10b981,color:#fff,stroke:#059669
    classDef decision fill:#fff,color:#000,stroke:#6b7280

    class START start
    class FIND,OPTIMIZE,GENERATE,SEQUENCE,GRAPH,DESIGN branch
    class BSEARCH,ROTATED,HASHMAP,BFS,DIJKSTRA,BELLMAN,ASTAR leaf
    class DP1D,DP2D,DPBIT,GREEDY,HEAP,HEAPMERGE leaf
    class SUBSETS,PERMS,COMBSUM,PLACEMENT leaf
    class FIXEDWIN,VARWIN,SUBSEQ,NEXTGT,NESTING leaf
    class COMPONENTS,DEPORDER,CYCLE,CLONE,MST,MAXFLOW leaf
    class LRU,MINSTACK,SORTEDDS,GENERIC leaf
    class SORTED,FINDGRAPH,OVERLAP,TOPK,CONTIG decision