丑数（Ugly Numbers,UVA 136）

#include<iostream>
#include<set>
#include<vector>
#include<queue>
using namespace std;
const int coeff[3]={2,3,5};
typedef long long LL;
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‘s ugly numbers 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);
			}
		}
	}
}