BeginnerBFS practice · C++17Best score: not submitted
Client-side educational grading. Submit runs your C++17 program against ten predefined tests in your browser. Tests are intentionally visible through See Hidden Tests. Scores are local practice records, not secure competition results.
Grading tests
C++ Suggestion Library
main.cpp · C++17
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Submission results
Ten tests, ten points each. Output is checked against the expected answer. Custom runs never change your score.
Test
Result
Points
Execution time
Each test has a 5-second execution limit, 256 MiB linked program WASM memory maximum, and 1 MiB combined output limit. Allocated WASM memory is not peak browser memory. Deep recursion can overflow the WASM stack; an iterative traversal is safer for long paths.
Problem statement
You are given an undirected, unweighted graph with N vertices and M edges. Find the minimum number of edges required to travel from vertex S to vertex T. If T cannot be reached from S, output -1.
Input format
First line: N M. Next M lines: U V. Last line: S T.
Output format
Print one integer: the minimum number of edges from S to T, or -1 if no path exists.
Constraints
1 ≤ N ≤ 100000
0 ≤ M ≤ 200000
1 ≤ U, V, S, T ≤ N
Self-loops and repeated edges are allowed.
Sample input
6 6
1 2
1 3
2 4
3 4
4 5
5 6
1 6
Sample output
4
Sample explanation
One shortest path is 1 → 2 → 4 → 5 → 6. It contains four edges.
Need a hint?
BFS with a distance array. Expected complexity: O(N + M).