丑数（UVa136）

　　

　　题目具体描述见：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=835&page=show_problem&problem=72

C++11代码如下：

#include<iostream>
#include<vector>
#include<set>
#include<queue>
using namespace std;

typedef long long LL;
const int coeff[3] = { 2,3,5 };
int main() {
    priority_queue<LL, vector<LL>, greater<LL> >pq;
    set<LL>s;
    pq.push(1);
    s.insert(1);
    for (int i = 1;; i++) {
        LL x = pq.top(); pq.pop();
        if (i == 1500) { 
            cout << "The 1500'th ugly number is " << x << '.' << endl;
            break;
        }
        for (int j = 0; j < 3; j++) {
            LL x2 = x * coeff[j];
            if (!s.count(x2)) { 
                s.insert(x2); 
                pq.push(x2);
            }
        }
    }
    return 0;
}