POJ_1251（kruskal算法）

POJ_1251，求最小生成树，这里采用基于并查集路径压缩的kruskal算法。
最小生成树有prim(适用于稠密图)和kruskal(适用于稀疏图)算法，
prim算法复杂度：v^2：每个(v)找直接相连边(v)
kruskal算法复杂度：eloge：将边按权值排序

#include  
#include  
#include 
using namespace std;
struct way{
	int v1ofway,v2ofway,cost;
};
way ways[80];
int father[30];

bool comp(way way1,way way2){
	return way1.cost<way2.cost;
}

int findfather(int v){
    int temp=v;
    while(v!=father[v]) 	v = father[v];	//查找
    //优化压缩路径
    while(temp!=father[temp]){
        int t_temp = temp;
        temp = father[temp];
        father[t_temp] = v;
    }
    return v;
}

int kruskal(int villagenum,int waynum){
	sort(ways,ways+waynum,comp);	//结构体数组排序写法 
	for(int i=0;i<villagenum;i++){
		father[i]=i;
	} 
	int cost=0;
	for(int i=0,j=0;j<villagenum-1;i++){
		int v1=ways[i].v1ofway;		int v2=ways[i].v2ofway;
		v1 = findfather(v1);		v2 = findfather(v2);
		if(v1!=v2){
			father[v2] = v1;
			j++;
			cost+=ways[i].cost;
		}
	}
	return cost;
}

int main(){
	int villagenum;
	while(cin>>villagenum){
		if(villagenum==0)	break;
		for(int i=0;i<80;i++){
			ways[i].v1ofway=0;	ways[i].v2ofway=0;	ways[i].cost=0;
		}
		for(int i=0;i<30;i++){
			father[i]=0;
		}
		int waynum=0;
		for(int i=0;i<villagenum-1;i++){
			char village1;	cin>>village1;
			int v1ways;		cin>>v1ways;
			for(int j=0;j<v1ways;j++){
				char village2;	cin>>village2;
				ways[waynum].v1ofway=village1-'A';
				ways[waynum].v2ofway=village2-'A';
				cin>>ways[waynum].cost;
				waynum++;
			}
		}
		cout<<kruskal(villagenum,waynum)<<endl;
	}
	return 0;
}