ZOJ2048最小生成树Kruskal算法

此算法在POJ上跑超时了，用了3s+;具体的思路和Prim算法一样

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define N 755

int rank[N],father[N];
int dis_sum, x[N], y[N];
typedef struct 
{
   int x, y;
   int w; 
}edge;
edge e[N*N];

int cmp(const void *a,const void *b)
{
    return (*(edge *)a).w > (*(edge *)b).w ? 1 : -1;
}   
    
int Make_set(int x)
{
    father[x] = x;    
    rank[x] = 0;
}    
    
int Find_set(int x)
{
    if(x != father[x] )
      father[x] = Find_set(father[x]);    
    return father[x];
}  
void Link(int x,int y,int w)
{
     if(rank[x] > rank[y])    
       father[y] = x;  
     else
     {   
        father[x] = y;   
        if(rank[x]==rank[y]) rank[y]++;
     } 
     dis_sum += w;
}
 
void Kruskal(int n,int m)
{    
   int i,x,y;  
   qsort(e,m,sizeof(edge),cmp);  
   dis_sum = 0;  
   for(i=1; i<=m; i++)  
   {  
      x = Find_set(e[i].x); 
      y = Find_set(e[i].y);
      if(x != y)
      {  Link(x,y,e[i].w);
        printf("%d %d\n",e[i].x,e[i].y);
      }
    }    
}     
     
int main()
{
    int i, j, towns, k;     
    int n,  a,  b,ncases; 
     
  scanf("%d",&ncases);
  while( ncases-- )
  {   
    scanf("%d",&towns); 
    for(i=1; i<=towns; i++) 
    { 
       scanf("%d%d",&x[i],&y[i]);
       Make_set(i);
    }
    k = 1;
    for(i=1; i<=towns; i++)
    for(j=1; j<=towns; j++)
    {
       e[k].x = i;
       e[k].y = j;
       e[k].w = (x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]);
       k++;
    }       
    
    scanf("%d",&n); 
    for(i=1; i<=n; i++) 
    {  
       scanf("%d%d",&a,&b);  
       a = Find_set(a);
       b = Find_set(b);
       Link(a,b,0);    
    }  
    Kruskal(towns,k-1);  
    if( ncases) printf("\n");
   }  
    return 0; 
}