hdu1863 畅通工程 基础最小生成树

 #include <iostream>
 #include <cstdio>
 #include <algorithm>
 #define N 110
 #define M 5000
 using namespace std;

 int n, m, u[M], v[M], w[M], r[M], p[N];
 bool cmp(int i, int j){ return w[i]<w[j]; }
 int f(int x){ return p[x] == x ? x : p[x] = f(p[x]); }

 int main()
 {
     while (cin >> m >> n&&m)
     {
         for (int i = ; i <= n; ++i) p[i] = i;
         for (int j = ; j <= m; ++j) r[j] = j;
         for (int j = ; j <= m; ++j) cin >> u[j] >> v[j] >> w[j];
         sort(r + , r +  + m, cmp);
         int ans = , k = ;
         for (int j = ; j <= m&&k<n - ; ++j)
         {
             int e = r[j]; int x = f(u[e]), y = f(v[e]);
             if (x != y)ans += w[e], ++k, p[x] = y;
         }
         if (k<n - )puts("?");
         else cout << ans << endl;
     }
     return ;
 }