(kruscal12.2.1)POJ 1258 Agri-Net(使用kruscal来计算最小边权值)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>


using namespace std;

struct edge{
	int begin;
	int end;
	int weight;
};

const int maxn = 110;
int father[maxn];
edge e[maxn*maxn];
int map[maxn][maxn];

int find(int x){
	if( x == father[x]){
		return x;
	}

	father[x] = find(father[x]);
	return father[x];
}

int kruscal(int count){//使用kruscal算法来生成最小生成树并计算带权路径和
	int i;
	int sum = 0;//用sum来记录最小s生成树的边权和

	for( i = 1 ; i < maxn ; ++i){
		father[i] = i;
	}

	for( i = 0 ; i < count ; ++i){//枚举有序边集中的每一条边
		int fx = find(e[i].begin);
		int fy = find(e[i].end);

		if(fx != fy){//若第k条边的两个端点i,j 分别属于两颗不同的子树
			father[fx] = fy;//则将节点i所在的子树并入节点j所在的子树中
			sum += e[i].weight;
		}
	}

	return sum;
}

bool compare(const edge& a , const edge& b){
	return a.weight < b.weight;
}

//以上是用kruscal算法来解决问题的基本模板.....

int main(){
	int n;
	while(scanf("%d",&n)!=EOF){

		int i,j;
		for(i = 1 ; i <= n ; ++i){
			for(j = 1 ; j <= n ; ++j){
				scanf("%d",&map[i][j]);
			}
		}



		int count = 0;
		for(i = 1 ; i <= n ; ++i){
			for(j = i+1 ; j <= n ; ++j){
				e[count].begin = i;
				e[count].end = j;
				e[count++].weight = map[i][j];
			}
		}

		sort(e,e+count,compare);//kruscal算法要求边有序

		int sum = kruscal(count);

		printf("%d\n",sum);
	}

	return 0;
}