识别信号
- Look for nodes with no incoming edges as a hint for mandatory inclusion.
- Consider in-degree counting to avoid full traversal of the DAG.
- The hint about thinking in reverse is a strong signal to identify which color could have been printed last.
解题流程
- 1. 明确窗口/状态定义
- 2. 更新状态并维护约束
- 3. 用边界样例验证
常见失分点
- Assuming any node can be included without checking in-degree may lead to non-minimal sets.
- Adding dependencies in the wrong direction is the most common bug; if color d appears inside color c's rectangle, then c must come before d.
- Double-counting a road that connects both cities when calculating network rank.
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