UVa 136 Ugly Numbers

Description

丑数是不能被2，3，5以外其他质数整除的数。
找第1500个丑数

Algorithm

生成丑数
每次取最小的丑数x，然后将2x,3x,5x加入优先队列

Code

#include <cstdio>
#include <iostream>
#include <queue>
#include <vector>
#include <set>
using namespace std;
typedef long long ll;
const 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);
  ll x;
  for (int i = 1; i <= 1500; i++)
  {
    x = pq.top();
    pq.pop();
    for (int j = 0; j < 3; j++)
    {
      ll x2 = x * a[j];
      if (!s.count(x2))
      {
        s.insert(x2);
        pq.push(x2);
      }
    }
  }
  cout << "The 1500'th ugly number is " << x << "." << endl;
}