畅通工程 hdu1863

http://acm.hdu.edu.cn/showproblem.php?pid=1863 

#include<iostream>//又是最小生成树的问题
#include<algorithm>
#include<cstdio>
using namespace std;
int s[4951];
 
 struct stu
 {
  int x;
  int y;
  int dis;
 }df[4951];

 int cmp(stu a, stu b)
 {
  return a.dis < b.dis;
 }

 int find (int a)
 {
  int r = a;
  while(r != s[r])
   r = s[r];
  return r;
 }

 void merge(int a, int b)
 {
  if(a > b)
   s[b] = a;
  else
   s[a] =b;
  
 }
int main()
{
 int n, m, q, i ,j, sum;
 while(scanf("%d%d", &n, &m) != EOF)
 {
  if(n ==0) continue;
  for(i = 0; i< n ;i++)
  {
   scanf("%d %d %d", &df[i].x, &df[i].y, &df[i].dis);
  }
  sort(df, df+n, cmp);
  for(i = 1; i <= n; i++)
    s[i] = i;
  q =0;
  sum = 0;
  for(i =0; i < n; i++)
  {
   int a = find(df[i].x);
   int b = find(df[i].y);
   if(a != b)
   {
    sum += df[i].dis;
    q++;
    merge(a , b);
   }
  }
  if(q == m-1)
    printf("%d/n", sum);
  else
    printf("?/n");
 }
 }