UVa 136 - Ugly Numbers

 1 // UVa136 Ugly Numbers
 2 // Rujia Liu
 3 // 代码由刘汝佳提供，我是在我的水平下，加以注释，学习大神的思想
 4 #include<iostream>
 5 #include<vector>
 6 #include<queue>
 7 #include<set>
 8 using namespace std;
 9 typedef long long LL;
10 const int coeff[3] = {2, 3, 5};
11 
12 int main() {
13   priority_queue<LL, vector<LL>, greater<LL> > pq;//越小的整数(LL)优先级越大的优先队列
14   set<LL> s;
15   pq.push(1);
16   s.insert(1);
17   for(int i = 1; ; i++) {
18     LL x = pq.top(); pq.pop();
19     if(i == 1500) {
20       cout << "The 1500‘th ugly number is " << x << ".\n";
21       break;
22     }
23     for(int j = 0; j < 3; j++) {
24       LL x2 = x * coeff[j];
25       if(!s.count(x2)) { s.insert(x2); pq.push(x2); }
26     }
27   }
28   return 0;
29 }