并查集-食物链（经典）

#include <iostream>
using namespace std;
const int maxn = 500010;
int animal[maxn];
int height[maxn];
int N, K;
void initGroup(int num) {
    for (int i = 1; i <= num; i++) {
        animal[i] = i;
    }
}
int findGroup(int x) {
    if (x != animal[x]) {
        animal[x] = findGroup(animal[x]);
    }
    return animal[x];
}

void unionGroup(int x, int y) {
    x = findGroup(x);
    y = findGroup(y);
    if (x != y) {
        animal[x] = y;
    }
}
int main() {
        int D, x, y;
        //这里注意不要用while(scanf("%d%d", &N, &K)!=EOF)会报答案错误，另外也不要使用 cin来输入，会超时
        scanf("%d%d", &N, &K);
        //animal[i]表示同种族的  animal[i+N]存i吃的 animal[i+2*N]表示i被吃的
        initGroup(N*3);
        int ans = 0;
        for (int i = 0; i < K; i++) {
            scanf("%d%d%d", &D, &x, &y);
            //cin >> D >> x >> y;
            if (x > N || y > N || (x == y&&D==2)||x<=0||y<=0) {
                ans += 1;
                continue;
            }
            if (D == 1) {
                if (findGroup(x) == findGroup(y + N) || findGroup(y) == findGroup(x + N)
                    || findGroup(x) == findGroup(y + 2*N)|| findGroup(y) == findGroup(x + 2*N)) {
                    ans += 1;
                    continue;
                }
                //x,y是同种动物
                else {
                    unionGroup(x, y);
                    unionGroup(x + N, y + N);
                    unionGroup(x + 2 * N, y + 2 * N);
                }
            }
            else{
                if (findGroup(x) == findGroup(y) || findGroup(x + 2 * N) == findGroup(y)) {
                    ans += 1;
                    continue;
                }
                //x吃y
                else {
                    unionGroup(x + N, y);
                    unionGroup(x, y + 2 * N);
                    unionGroup(x + 2 * N, y + N);
                }
            }    
        }
        cout << ans << endl;
        return 0;
}