I. 【图的遍历】图的遍历

Type: Default

1000ms

256MiB

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题目描述

给出一有向图，包含n个点，编号从1-n，m条边，询问是否能从a点走到b点

第一行4个整数n,m,a,b 接下来m行，每行2个整数x，y，表示x到y有一条有向边

如果能走到输出Yes，否则输出No

3 2 1 3
1 2
2 3

Yes

3 2 1 3
1 2
2 1

No

$0<n,m<=200000,a,b,x,y保证合法$