* 时间O(n) 空间O(n)（理论最优，无冗余计算）
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專家警告，AI企業在開發更強大工具時，往往優先考量技術而非人權，且在未支付費用的情況下使用數據。，更多细节参见夫子
Shortcuts: For common scenarios, we pre-calculate the travel time/distance (the "shortcut") between border points within the same cluster and also to border points of immediately adjacent clusters.