AcWing：240. 食物链（扩展域并查集）

#include 
#include using namespace std;

const int maxn = 3e5+7;

int f[maxn];

int get(int x) {
    if(x == f[x]) {
        return f[x];
    }
    int root = get(f[x]);
    return f[x] = root;
}

int main() {
    int n, m;
    scanf("%d %d", &n, &m);
    for(int i = 1; i 3 * n; i++) {
        f[i] = i;
    }
    int ans = 0;
    while(m--) {
        int op, x, y;
        scanf("%d %d %d", &op, &x, &y);
        int x_self = x, x_eat = x + n, x_enemy = x + n + n;
        int y_self = y, y_eat = y + n, y_enemy = y + n + n;
        if(x > n || y > n) {    //动物编号不存在
            ans++;
        } else if(op == 1) {    //x和y是同类关系
            if(get(x_eat) == get(y_self) || get(x_self) == get(y_eat)) {    //如果x捕食的物种和y的同类在同一集合，或者x的同类和y捕食的物种在同一集合，那么不成立，此话是假
                ans++;
            } else {    //合并同类物种
                f[get(x_self)] = get(y_self);
                f[get(x_eat)] = get(y_eat);
                f[get(x_enemy)] = get(y_enemy);
            }
        } else {    //x和y是捕食关系，x吃y
            if(get(x_self) == get(y_self) || get(x_self) == get(y_eat)) {    //如果x的同类和y的同类在同一集合，或者x的同类和y捕食的物种在同一集合，那么不成立，此话是假
                ans++;
            } else {    //合并同类物种
                f[get(x_eat)] = get(y_self);
                f[get(x_self)] = get(y_enemy);
                f[get(x_enemy)] = get(y_eat);
            }
        }
    }
    printf("%d\n", ans);
    return 0;
}