(step5.1.5)hdu 1856(More is better——DFS)

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题目大意:输入一个整数n，表示有n对朋友，接下来给出n对朋友。。。输出最大的集合中的人数(即，秋季喝的最大的秩)

解题思路:并查集

1)按秩的大小来插。即

if( fx != fy){//这里根据秩的大小来插入if(rank[fx] > rank[fy]){rank[fx] += rank[fy];father[fy] = fx;}else{rank[fy] += rank[fx];father[fx] = fy;}}

2)需要求出秩的最大值

int max = -1;for( i = 1 ; i<= 10000001 ; ++i){if(rank[i] > max){max = rank[i];}}

代码如下:

/* * 1856_2.cpp * *  Created on: 2013年8月23日 *      Author: Administrator */#include <iostream>using namespace std;/** * father[i] :用来保存当前节点的父亲节点 * rank[i] :用来保存当前节点的秩(即当前节点包含了多少节点) * */int father[10000001];int rank[10000001];int find(int a){if( a == father[a]){return a;}     father[a] = find(father[a]);     return father[a];}void join(int x , int y){int fx = find(x);int fy = find(y);if( fx != fy){//这里根据秩的大小来插入if(rank[fx] > rank[fy]){rank[fx] += rank[fy];father[fy] = fx;}else{rank[fy] += rank[fx];father[fx] = fy;}}}void make_set(){int i;for( i = 1 ; i<= 10000001 ; ++i){father[i] = i;rank[i] = 1;}}int main(){int n;while(scanf("%d",&n)!=EOF){memset(rank,0,sizeof(rank));memset(father,0,sizeof(father));make_set();int i;for( i = 1 ; i <= n ; ++i ){int a,b;scanf("%d%d",&a,&b);join(a,b);}//以下代码用来求秩的最大值int max = -1;for( i = 1 ; i<= 10000001 ; ++i){if(rank[i] > max){max = rank[i];}}printf("%d\n",max);}}