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QOJ

Type: Editorial

Status: Open

Posted by: jiangly

Posted at: 2025-12-13 00:06:24

Last updated: 2025-12-13 00:06:26

Back to Problem

容易发现充要条件是存在如下三种情况之一：

.ab
ab.

.a
ab
b.

.a..
a...
...b
..b.

扫一遍即可，时间复杂度 $O(nm)$。

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