WA #9 || 并查集做法 || 萌新求助

#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 5;
int cnt;
int nxt[maxn << 1], hed[maxn << 1], ver[maxn << 1], pre[maxn << 1];
void adde(int u, int v) {
	cnt++;
	pre[cnt] = u;
	ver[cnt] = v;
	nxt[cnt] = hed[u];
	hed[u] = cnt;
	return;
}
int f[maxn];
int find(int x) {
	return x == f[x] ? x : f[x] = find(f[x]);
}
int n, m, k;
int od[maxn], bo[maxn];
int ans[maxn];
signed main() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++) f[i] = i;
	for (int i = 1; i <= m; i++) {
		int u, v;
		scanf("%d%d", &u, &v);
		adde(u, v);
		adde(v, u);
	}
	scanf("%d", &k);
	for (int i = 1; i <= k; i++) {
		scanf("%d", &od[i]);
		bo[od[i]] = 1;
	}
	int tot = n - k;
	for (int i = 1; i <= m << 1; i++) { //???
		int u = pre[i];
		int v = ver[i];
		if (bo[u] == 0 && bo[v] == 0) {
			if (f[find(u)] != f[find(v)]) {
				tot--;
				f[find(u)] = f[find(v)];
			}
		}
	}
	ans[k + 1] = tot;
	for (int i = k; i >= 1; i--) {
		int u = od[i];
		tot++;
		bo[u] = 0;
		for (int j = hed[u]; j; j = nxt[j]) {
			int v = ver[j];
			if (bo[v] == 0 && f[find(u)] != f[find(v)]) {
				tot--;
				f[find(u)] = f[find(v)];
			}
		}
		ans[i] = tot;
	}
	for (int i = 1; i <= k + 1; i++) {
		printf("%d\n", ans[i]);
	}
	return 0;
}