普利姆算法（最小生成树）

int prim(){
    int minid, i, j;
    double mincost;
    for(i = 2; i <= n; i ++){
        lowcost[i] = map[1][i];
    }
    lowcost[1] = -1;
    for(i = 2; i <= n; i ++){
        mincost = INF;
        minid = 0;
        for(j = 2; j <= n; j ++){
            if(lowcost[j] < mincost && lowcost[j] > 0){
                mincost =  lowcost[j];
                minid = j;
            }
        }
        if(minid == 0){
            return 1;
        }
        weight[i] = mincost;
        lowcost[minid] = -1;
        for(j = 2; j <= n; j ++){
            if(map[minid][j] < lowcost[j]){
                lowcost[j] = map[minid][j];
            }
        }
    }
    return 0;
}