并查集

并查集在解决图的连通性非常高效，hdu1232采用并查集，可以很快解决，代码如下：

/* * hdu1232.cpp * *  Created on: 2012-5-10 *      Author: ict */#include<iostream>#include<cstring>#include<cstdio>#include<cmath>#include<algorithm>using namespace std;#define CLR(arr, what) memset(arr, what, sizeof(arr))#define N 1001int pre[N];int Find_Set(int x) //递归+路径压缩{return pre[x] == -1 ? x : (pre[x] = Find_Set(pre[x]));}void Make_Set(int x, int y) //无按秩合并{int root1 = Find_Set(x);int root2 = Find_Set(y);if(root1 != root2)pre[root2] = root1;}int main(){int i, j;int n, m;int a, b;int count;while(1){scanf("%d", &n);if(!n)break;scanf("%d", &m);CLR(pre, -1);for(i = 0; i < m; i++){scanf("%d %d", &a, &b);Make_Set(a, b);}count = 0;for(i = 1; i <= n; i++){if(pre[i] == -1)count++;}printf("%d\n", count - 1);}return 0;}