pku 3253 Fence Repair 优先队列实现哈夫曼树

http://poj.org/problem?id=3253

#include <cstdio>
#include <cstring>
#include <queue>
#include <iostream>
#define maxn 20007
using namespace std;

struct cmp
{
   bool operator() (int &a,int &b)
   {
       return a > b;
   }
};
int main()
{
    priority_queue<int,vector<int>,cmp>q;
    int n,i,sum,a;
    while (~scanf("%d",&n))
    {
        while (!q.empty()) q.pop();
        for (i = 0; i < n; ++i)
        {
            scanf("%d",&a);
            q.push(a);
        }
        sum = 0;
       while (!q.empty())
       {
           int x = q.top(); q.pop();
           int y = q.top(); q.pop();
           //printf("%d %d\n",x,y);
           sum += (x+y);
           if (!q.empty())
           q.push(x + y);
       }
       printf("%d\n",sum);
    }
}