poj1182食物链（并查集）

好博客~ （队友博客推荐）

运用向量传递关系的思想，太妙了~

 

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
const int maxn = 50010;
struct Node
{
    int pre;
    int relation;

}p[maxn];
int n, k;

int findfa(int x)
{
    int temp;
    if(x == p[x].pre)
        return x;

    temp = p[x].pre;
    p[x].pre = findfa(temp);
    p[x].relation = (p[x].relation + p[temp].relation) % 3;     //great
    return p[x].pre;
}

void init()
{
    for(int i = 1; i <= n; i++)
    {
        p[i].pre = i;
        p[i].relation = 0;
    }
}


int main()
{
    int ope, a, b;
    cin >> n >> k;
    int sum = 0;
    init();

    for(int i = 1; i <= k; i++)
    {
        scanf("%d%d%d", &ope, &a, &b);
        if(a > n || b > n)
        {
            sum++;
            continue;
        }
        if(ope == 2 && a == b)
        {
            sum++;
            continue;
        }
        int root1, root2;
        root1 = findfa(a);
        root2 = findfa(b);
        if(root1 != root2)
        {
            p[root2].pre = root1;
            p[root2].relation = (p[a].relation + (ope - 1) + 3 - p[b].relation) % 3;
        }
        else
        {
            if(ope == 1 && p[a].relation != p[b].relation)
            {
                sum++;
                continue;
            }
            else if(ope == 2 && (p[a].relation + (ope - 1) + 3 - p[b].relation) % 3 != 0)
            {
                sum++;
                continue;
            }

        }
    }
    cout << sum << endl;
    return 0;
}