POJ 1182 食物链——种类并查集

感觉这种题型快忘了，拿出来复习一下。

https://blog.csdn.net/niushuai666/article/details/6981689

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int maxn = 5e4 + 10;

struct Node {
    int fa;
    int rel;
}node[maxn];

void init(int n) {
    for (int i = 1; i <= n; i++) {
        node[i].fa = i;
        node[i].rel = 0;
    }
}

int query(int x) {
    if (x == node[x].fa) return x;
    int y = node[x].fa;
    node[x].fa = query(y);
    node[x].rel = (node[y].rel + node[x].rel) % 3;
    return node[x].fa;
}

int main() {
    int n, k;
    scanf("%d%d", &n, &k);
    init(n);
    int d, x, y, ans = 0;
    while (k--) {
        scanf("%d%d%d", &d, &x, &y);
        if (x > n || y > n) ans++;
        else if (d == 2 && x == y) ans++;
        else {
            int rx = query(x), ry = query(y);
            if (rx == ry) {
                if ((3 - node[x].rel + node[y].rel) % 3 != d-1) ans++;
            }
            else {
                node[ry].fa = rx;
                node[ry].rel = (node[x].rel + d - 1 + 3 - node[y].rel) % 3;
            }
        }
    }
    printf("%d\n", ans);
    return 0;
}