UVALive - 3644 X-Plosives (并查集)

思路：每一个product都可以作一条边，每次添加一条边，如果这边的加入使得某个集合构成环，就应该refuse，那么就用并查集来判断。

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AC代码：

//#define LOCAL
#include <stdio.h>
#include <string.h>
const int maxn = 1e5 + 5;
int par[maxn], rank[maxn];

void init() {
    memset(rank, 0, sizeof(rank));
    for(int i = 0; i <= maxn; i++) {
        par[i] = i;
    }
}

int findRoot(int x) {
    return x != par[x] ? par[x] = findRoot(par[x]) : x;
}

//启发式合并
void unionSet(int x, int y) {
    if(rank[x] > rank[y]) {
        par[y] = x;
    } else {
        par[x] = y;
        if(rank[x] == rank[y]) rank[y]++;
    }
}

int main() {
#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif // LOCAL

    int x, y, refuse = 0;
    init();
    while(scanf("%d", &x) == 1) {
        if(x == -1) {
            printf("%d\n", refuse);
            init();
            refuse = 0;
        }else {
            scanf("%d", &y);
            x = findRoot(x);
            y = findRoot(y);
            if(x == y) {
                //refuse it
                refuse++;
            } else {
                //union
                unionSet(x, y);
            }
        }
    }
    return 0;
}

如有不当之处欢迎指出！