hdu 1102 Constructing Roads

此题是最小生成树的基础题

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int set[124],n,t,a,b,c;
long long min;
struct map
{
       int x,y,val;
}m[ 100000 ];
int cmp( const void *a,const void *b )
{
    return ( ( map * ) a ) -> val - ( ( map * ) b ) -> val;
}
int find( int i )
{
    return set[ i ] == i ? i :set[ i ] = find( set[ i ] );
}
void merge( int x,int y )
{
     int a = find( x ),b = find( y );
     if( a != b )
         set[ a ] = b;
 }
void K( )
{
     for( int i = 1;i <= c; ++i )
     {
          int a = find( m[ i ].x ),b = find( m[ i ].y ),val = m[ i ].val;
          if( a != b )
          {
              set[ a ] = b;
              min += val;
          }
      }
 }
int main( )
{
    while( scanf( "%d",&n ) != EOF )
    {
           for( int i = 1; i <= 123 ; ++i )
                set[ i ] = i;
           c = 1;
           for( int i = 1; i <= n; ++i )
           {
                for( int j = 1 ; j <= n; ++j )
                {
                     int val;
                     scanf( "%d", &val );
                     if( j >= i  )//因为矩阵是对称的所以只要存入一半就可以了 
                     {
                         m[ c ].x = i;
                         m[ c ].y = j;
                         m[ c ].val = val;
                         ++c;
                         }
                 }
            }
            qsort( m + 1,c,sizeof( m[ 0 ] ),cmp );
            scanf( "%d",&t );
            while( t-- )
            {
                   scanf( "%d%d",&a,&b );
                   merge( a,b );//将以连接的合并成一个集合 
                   }
            min = 0;
            K(  );
            printf( "%I64d\n",min );
           }
    return 0;
}