UVA - 136 Ugly Numbers

Ugly Numbers

Time Limit: 3000MS Memory Limit: Unknown 64bit IO Format: %lld & %llu

SubmitStatus

Description

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>.

熟悉一下队列

#include <iostream>
#include <set>
#include <queue>
#include <vector>
using namespace std;
int book[]={2, 3, 5};
typedef long long LL;


int main()
{
    set<LL>s;
    priority_queue<LL,vector<LL>,greater<LL> >pq;
    s.insert(1);
    pq.push(1);
    for(int i=1;;i++)
    {
        LL x=pq.top();
        pq.pop();
        if(i==1500)
        {
            cout<<"The 1500'th ugly number is "<<x<<"."<<endl;
            break;
        }
        for(int j=0;j<3;j++)
        {
            LL x2=x*book[j];
            if(!s.count(x2))
            {
                s.insert(x2);
                pq.push(x2);
            }
        }
    }
    return 0;
}