畅通工程 (最小生成树）（最短路径和）

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define s(x) scanf("%d",&x)
#define sc(x,y) scanf("%d %d",&x,&y)
#define sca(x,y,z) scanf("%d %d %d",&x,&y,&z)
const int mxn = 1e2+5,inf = 0x3fffffff;

int n,m,c,r,k,arr[mxn][mxn],dis[mxn],vis[mxn];
int prim(int now)
{
    fill(dis,dis+mxn,inf);
    fill(vis,vis+mxn,0);
    int ans = 0;dis[now] = 0;
    for(int i=1;i<=m;i++)
    {
        int index = -1 , mn = inf;
        for(int j=1;j<=m;j++)
        {
            if(!vis[j] && mn>dis[j])
            {
                mn = dis[j];
                index = j;
            }
        }
        if(index == -1) return -1;
        vis[index] = 1;
        ans += dis[index];
        for(int k=1;k<=m;k++)
            if(!vis[k] && dis[k]>arr[index][k])
                dis[k] = arr[index][k];
    }
    return ans;
}
int main()
{
    while(~sc(n,m))
    {
        if(!n) break;
        fill(arr[0], arr[0] + mxn * mxn, inf);
        for(int i=1;i<=n;i++)
        {
            sca(c,r,k);
            arr[c][r] = k;arr[r][c] = k;
        }
        prim(1)==-1?printf("?\n"):printf("%d\n",prim(1));
    }
    return 0;
}