UVA 136 Ugly Numbers

Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence

1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, ...

shows the first 11 ugly numbers. By convention, 1 is included.

Write a program to find and print the 1500'th ugly number.

Input and Output

There is no input to this program. Output should consist of a single line as shown below, with <number> replaced by the number computed.

Sample output

The 1500'th ugly number is <number>.
#include<iostream>
#include<vector>
#include<queue>
#include<set>
using namespace std;

const int c[3] = {2, 3, 5};
priority_queue<long long,vector<long long>,greater<long long> >pq;
set<long long> s;

int main() {
pq.push(1);
s.insert(1);
long long x;
for(int i = 1; i<=1500; i++) {
x = pq.top(); pq.pop();
for(int j = 0; j < 3; j++)
{
long long x2 = x * c[j];
if(s.count(x2)==0) {
s.insert(x2); pq.push(x2);
}
}
}
cout << "The 1500'th ugly number is " << x<< "."<<endl;
return 0;
}