Kruskal 算法

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
const int inf = 0x7fffffff;
int st[110], rank[110], N, M, x, y, val, maxN, map[110][110];
struct Edge {
    int x, y, val;
}e[10000];
int cmp ( const void *a, const void *b ) {
    return (( Edge * )a)->val - ( ( Edge * )b )->val;   
}
int find ( int i ) {
    return i == st[i] ? i : st[i] = find ( st[i] );   
}
void merge ( int x, int y ) {
    int a = find ( x ), b = find ( y );
    if ( a != b ) {
        st[a] = b;
        rank[b] += rank[a];   
        //maxN >?= rank[b];
        if ( maxN < rank[b] ) maxN = rank[b];
    }
}
int Kruskal () {
    int sum = 0;
    for ( int i = 0 ; i < N; ++ i ) {
        int x = e[i].x, y = e[i].y, val = e[i].val;
        if ( find ( x ) != find ( y ) ) {
            sum += val;
            merge ( x, y );   
        }   
    }   
    return sum;
}
int main()
{
    while ( scanf ( "%d%d", &N, &M ) != EOF && N ) {
        maxN = 0;
        for ( int i = 0; i <= M; ++ i ) {
            st[i] = i;
            rank[i] = 1;
            for ( int j = 0; j <= M ; ++ j ) {
                map[i][j] = inf;   
            }   
        }
        for ( int i = 0; i < N; ++ i ) {
            scanf ( "%d%d%d", &x, &y, &val );
            //map[x][y] = map[y][x] = val;
            e[i].x = x, e[i].y = y, e[i].val = val;   
        }    
        qsort ( e, N, sizeof ( e[0] ), cmp ); puts(" --------------------->");
        int res = Kruskal ();
        if ( maxN < M ) puts ( "?" );
        else printf ( "%d\n", res );
    }
//    system("pause");
    return 0;