Date: 2026-06-06
Time: 16:38
find-if-path-exists-in-graph/solution.pyThis file solves LeetCode 1971 — Find if Path Exists in Graph. It determines whether two nodes in an undirected graph are connected. The file owns both the solution and its inline unit tests — a self-contained module following the repo's per-problem convention.
memstickscrash(n, edges, source, destination) -> bool — The main solver. Despite the misleading name (likely an artifact of automated generation or obfuscation), this implements a classic Union-Find to answer graph connectivity queries. Its contract:
n nodes labeled 0..n-1, a list of undirected edges [u, v], and two node indices source/destination.True if any path connects source to destination, False otherwise.parent/rank arrays).find(x) -> int — Inner closure. Walks the parent chain to locate the root representative of x's component. Uses iterative path splitting (setting parent[x] = parent[parent[x]] each step) — a one-pass path-halving optimization, not full recursive path compression.
union(a, b) -> None — Inner closure. Merges the components containing a and b using union by rank. The higher-rank root becomes the new parent, and rank increments only on ties.
TestMemSticksCrash — Seven test cases covering: both LeetCode examples, identity (source == destination), empty edges, single edge, disconnected components, and a chain graph.
parent[x] = parent[parent[x]]) is a lighter alternative to full path compression — it halves the path length each traversal rather than flattening it completely. Combined with union by rank, amortized cost per operation is effectively O(α(n)).find and union close over parent and rank, avoiding a class while keeping state local to a single invocation.if _name == "main_": unittest.main()), following the repo-wide pattern of colocating solution + tests in the same directory.Imports: Only unittest from the standard library — no external dependencies.
Imported by: The "Imported By" list in the prompt is misleading. Those ~400+ test files don't actually import *this* file — that list appears to be a repo-wide artifact (possibly all test files that share a common test harness pattern). The real consumer is find-if-path-exists-in-graph/testsolution.py, which imports memsticks_crash from this module.
1. Initialize parent[i] = i (each node is its own root) and rank[i] = 0.
2. Process every edge [u, v] by calling union(u, v), which merges their components.
3. After all edges are processed, check find(source) == find(destination) — same root means connected.
The entire edge list is consumed before the query. This is a batch approach: O(n + E·α(n)) total, where E is the number of edges. For a single source/destination query this is fine; BFS/DFS would also work but Union-Find is equally efficient here and more naturally extends to multiple queries.
parent array represents a forest of up-trees: parent[x] == x iff x is a root. After union, exactly one root exists per connected component.rank[root] only increments when merging equal-rank trees, ensuring logarithmic tree depth before path compression.parent[x] = parent[parent[x]] only redirects x to its grandparent — it never crosses component boundaries, so find still returns the correct root.source, destination, and all edge endpoints are in [0, n).None. Invalid inputs (negative n, out-of-range node indices, non-list edges) will raise IndexError or TypeError at runtime. This is standard for LeetCode solutions where input validity is guaranteed by the problem constraints.