【HDOJ】2473 Junk-Mail Filter

并查集删除结点，方法是构建虚拟点，做映射。

#include <stdio.h>
#include <string.h>

#define MAXNUM 1000050

int bin[MAXNUM], assist[MAXNUM];
char visit[MAXNUM];
int n, ext;

int find(int x) {
    int r = x;
    int i = x, j;

    while (r != bin[r])
        r = bin[r];

    while (i != r) {
        j = bin[i];
        bin[i] = r;
        i = j;
    }

    return r;
}

void merge(int x, int y) {
    int fx, fy;

    fx = find(x);
    fy = find(y);

    if (fx != fy) {
        bin[fx] = fy;
    }
}

void extract(int x) {
    bin[ext] = ext;
    assist[x] = ext++;
}

int main() {
    int m, t=1;
    int i, x, y;
    char ch;

    while (scanf("%d %d", &n, &m)!=EOF && (n||m)) {
        memset(bin, 0, sizeof(bin));
        memset(assist, 0, sizeof(assist));
        memset(visit, 0, sizeof(visit));
        for (i=0; i<n; ++i) {
            bin[i] = i;
            assist[i] = i;
        }
        ext = n;
        while (m--) {
            scanf("%*c%c", &ch);
            if (ch == 'M') {
                scanf("%d %d", &x, &y);
                x = assist[x];
                y = assist[y];
                merge(x, y);
            } else {
                scanf("%d", &x);
                extract(x);
            }
        }
        m = 0;
        for (i=0; i<n; ++i) {
            x = find(assist[i]);
            if (visit[x] == 0) {
                ++m;
                visit[x] = 1;
            }
        }
        printf("Case #%d: %d\n", t++, m);
    }

    return 0;
}