poj 1251 MST

最小生成树模板。注意读入方法。

输入：

9
A 2 B 12 I 25
B 3 C 10 H 40 I 8
C 2 D 18 G 55
D 1 E 44
E 2 F 60 G 38
F 0
G 1 H 35
H 1 I 35
3
A 2 B 10 C 40
B 1 C 20
0

输出：

216
30

#include <stdio.h>
#include <string.h>
#define N 30
#define MaxRoad 78
#define INF 0x3fffffff
int n,top;
struct egge{
	int y,w,next;
}e[MaxRoad*2];
int first[N],dis[N],visited[N];
void init(){
	int i;
	top = 0;
	memset(visited,0,sizeof(visited));
	memset(first,-1,sizeof(first));
	for(i = 1;i<N;i++)
		dis[i] = INF;
}
void add(int x,int y,int w){
	e[top].y = y;
	e[top].w = w;
	e[top].next = first[x];
	first[x] = top++;
}
int prim(){
	int i,j,min,pos,res=0;
	for(i = first[1];i!=-1;i=e[i].next)
		dis[e[i].y] = e[i].w;
	visited[1] = 1;
	for(i = 1;i<n;i++){
		min = INF;
		for(j = 1;j<=n;j++)
			if(!visited[j] && dis[j]<min){
				pos = j;
				min = dis[j];
			}
		res += min;
		visited[pos] = 1;
		for(j=first[pos];j!=-1;j=e[j].next)
			if(!visited[e[j].y] && e[j].w<dis[e[j].y])
				dis[e[j].y] = e[j].w;
	}
	return res;
}
int main(){
	freopen("a.txt","r",stdin);
	while(scanf("%d",&n) && n){
		int i,j,w,num;
		char ch;
		init();
		for(i = 1;i<n;i++){
			scanf(" %c %d",&ch,&num);
			while(num--){
				scanf(" %c %d",&ch,&w);
				j = ch-'A'+1;
				add(i,j,w);
				add(j,i,w);
			}
		}
		printf("%d\n",prim());
	}
	return 0;
}