http://www.lydsy.com/JudgeOnline/problem.php?id=4579

把时间倒过来，只是加点，并查集维护连通块。

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

const int N = 200003;

struct node {int nxt, to;} E[N << 1];

int a[N], tot = 0, n, m, cnt = 0, point[N], fa[N];

bool mark[N], op[N];

void ins(int u, int v) {

	E[++cnt] = (node) {point[u], v}; point[u] = cnt;

}

int find(int x) {return x == fa[x] ? x : fa[x] = find(fa[x]);}

int main() {

	scanf("%d%d", &n, &m);

	int u, v;

	for (int i = 1; i <= m; ++i) {

		scanf("%d%d", &u, &v);

		ins(u, v); ins(v, u);

	}

	for (int i = 1; i <= n; ++i) scanf("%d", a + i), fa[i] = i;

	for (int i = n; i >= 1; --i) {

		mark[a[i]] = true;

		++tot;

		for (int j = point[a[i]]; j; j = E[j].nxt)

			if (mark[E[j].to] && (u = find(E[j].to)) != (v = find(a[i])))

				fa[u] = v, --tot;

		if (tot == 1)

			op[i] = true;

		else

			op[i] = false;

	}

	for (int i = 1; i <= n; ++i)

		puts(op[i] ? "YES" : "NO");

	return 0;

}