uva 136 120页

#include <queue>
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <set>
#define ll long long 
using namespace std;
int a[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++) {
        if(1500==i) {
            printf("The 1500'th ugly number is %lld.\n",pq.top());
            break;
        }
        else {
            ll t=pq.top();pq.pop();
            for(int j=0;j<3;j++) {
                ll num=a[j]*t;
                if(!s.count(num)) {
                    s.insert(num);
                    pq.push(num);
                }
            }
        }
    } 
    return 0;
}