并查集详解

 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
int pre[1010]; //里面全是掌门
 
int unionsearch(int root)
{
    int son, tmp;
    son = root;
    while(root != pre[root]) //寻找掌门ing……
        root = pre[root];
    while(son != root) //路径压缩
    {
        tmp = pre[son];
        pre[son] = root;
        son = tmp;
    }
    return root; //掌门驾到~
}
 
int main()
{
    int num, road, total, i, start, end, root1, root2;
    while(scanf("%d%d", &num, &road) && num)
    {
        total = num - 1; //共num-1个门派
        for(i = 1; i <= num; ++i) //每条路都是掌门
            pre[i] = i;
        while(road--)
        {
            scanf("%d%d", &start, &end); //他俩要结拜
            root1 = unionsearch(start);
            root2 = unionsearch(end);
            if(root1 != root2) //掌门不同？踢馆！~
            {
                pre[root1] = root2;
                total--; //门派少一个，敌人（要建的路）就少一个
            }
        }
        printf("%d\n", total);//天下局势：还剩几个门派
    }
    return 0;
}