还是畅通工程

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int MAX = 5000;
struct edge{
    int s;
    int e;
    int w;
}a[MAX];
bool cmp(edge a,edge b){
    return a.w < b.w;
}
int p[MAX];
int find(int x){
 return x == p[x]?x:p[x] = find(p[x]);
 }
 int main()
 {
     int N,M;
     while(~scanf("%d",&N)&&N){
            M = N*(N-1)/2;
          memset(p,0,sizeof(p));
          memset(a,0,sizeof(a));
          for(int i = 1; i <= N;i++)
             p[i] = i;
          for(int i = 1 ; i<= M;i++)
            scanf("%d%d%d",&a[i].s,&a[i].e,&a[i].w);
          sort(a+1,a+M+1,cmp);
          int sum = 0;
          for(int i = 1;i <= M ;i++){
                int fx = find(a[i].s),fy = find(a[i].e);
           if(fx!=fy){
            p[fx] = fy;
           sum +=a[i].w;
            }
        }
        printf("%d\n",sum);
     }
     return 0;
 }