[JSOI2008]星球大战starwar

黑书上猴子内个题 逆向思维真是吊

#include <cstdio>
#include <cstring>
const int N = 500000, M = 500000;
int key[M], head[N], next[M], cnt;
int a[N], p[N], ans[N];
bool v[N];
inline void add (const int & x, const int & y)
{
    key[cnt] = y;
    next[cnt] = head[x];
    head[x] = cnt ++;
}
inline int F (int x) { return p[x] == x ? x : p[x] = F (p[x]); }
int main ()
{int n, m;memset (head, -1, sizeof head);
    scanf ("%d%d", &n, &m);
    for (int i = 1, a, b; i <= m; i ++)
        scanf ("%d%d", &a, &b), add (a, b), add (b, a);int k;
    scanf ("%d", &k);
    for (int i = 1; i <= k; i ++)
        scanf ("%d", &a[i]), v[a[i]] = true;
    for (int i = 1; i <= n; i ++)
        p[i] = i;
    int z = n - k;
    for (int i = 0; i < n; i ++)
        if (!v[i])
            for (int j = head[i]; ~ j; j = next[j])
                if (!v[key[j]])
                    if (F (i) != F (key[j]))
                        p[F (i)] = F (key[j]), z --;
    ans[k + 1] = z;
    for (int i = k; i >= 1; i --)
    {
        v[a[i]] = false;    
        z ++;
        for (int j = head[a[i]]; ~ j; j = next[j])
            if (!v[key[j]])
                if (F (a[i]) != F (key[j]))
                    p[F (a[i])] = F (key[j]), z --;
        ans[i] = z;
    }
    for (int i = 1; i <= k + 1; i ++)
        printf ("%d\n", ans[i]);
    return 0;
}