【BZOJ 4579】【Usaco2016 Open】Closing the Farm

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;
}