POJ 1182 食物链 (带权并查集写法)

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https://vjudge.net/problem/POJ-1182

当个带权并查集模板吧，解决问题的关键在于在向量之间确立联系，并且保证这种联系符合向量运算法则

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<cmath>
#define ll long long
#define mod 1000000007
#define inf 0x3f3f3f3f
using namespace std;
const int maxn = 50005;
int pre[maxn], val[maxn];
int find(int x)
{
    if(pre[x] != x)
    {
        int tmp = pre[x];
        pre[x] = find(pre[x]);
        val[x] = (val[x] + val[tmp]) % 3;
    }
    return pre[x];
}
int main()
{
    int n, m;
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i ++)
    {
        pre[i] = i;
        val[i] = 0;
    }
    int u, v, w;
    int ans = 0;
    for(int i = 1; i <= m; i ++)
    {
        scanf("%d%d%d", &w, &u, &v);
        if(u > n || v > n || (w == 2 && u == v))
            ans ++;
        else
        {
            int fu = find(u), fv = find(v);
            if(fu == fv)
            {
                if((w - 1) != ((val[u] - val[v] + 3) % 3))
                    ans ++;
            }
            else
            {
                pre[fu] = fv;
                val[fu] = (w - 1 + val[v] - val[u]) % 3;
            }
        }
    }
    printf("%d\n", ans);
    return 0;
}