CustomCC0-1.0#cpq013-9212400
Sparse Graph Reversal Distance
Summary
- •Phase 5 / 0-1-bfs, graph
- •Reasoning-first competitive programming drill
Problem Description
Given a directed graph with N nodes and M edges, and Q queries (U, V), find the minimal number of edge reversals needed to have a path from U to V.
How to read this problem in plain language:
- This is a Phase 5 reasoning drill focused on 0-1-bfs, graph.
- Typical lenses to test first: graph, bfs, edge-reversal.
- Constraints reminder: 1 <= N, Q <= 1e5; 0 <= M <= 2e5; 1 <= u, v, U, V <= N
Mini examples for mental simulation:
1) Boundary example: Describe why this case is tricky. Explain expected behavior and why naive logic may fail.
2) Adversarial example: Adversarial case where naive greedy/local decision looks correct but fails globally.
Lite-mode writing target:
- Write 1~2 observations that shrink the search space.
- Name one final algorithm and state target complexity explicitly.
- Validate with at least 2 edge cases and one hand simulation.
Constraints
- •1 <= N, Q <= 1e5; 0 <= M <= 2e5; 1 <= u, v, U, V <= N
Analysis
Key Insight
Use this hint to refine your reasoning. This step should reduce search space or formalize correctness. State why this insight changes your algorithm choice.
graphbfsedge-reversal