POJ

Ugly Numbers

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 24517 Accepted: 10837

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, ...
shows the first 10 ugly numbers. By convention, 1 is included.
Given the integer n,write a program to find and print the n'th ugly number.

Input

Each line of the input contains a postisive integer n (n <= 1500).Input is terminated by a line with n=0.

Output

For each line, output the n’th ugly number .:Don’t deal with the line with n=0.

Sample Input

1290

Sample Output

1210 找规律，每次求出一个最小的并标记，看代码吧。。
#include<iostream>#include<algorithm>using namespace std;int main(){    int ans[1509]= {1};    int x2=0,x3=0,x5=0;    for(int i=1;i<=1501; i++)        {            int com[3]={ans[x2]*2,ans[x3]*3,ans[x5]*5};            sort(com,com+3);            ans[i]=com[0];            if(ans[i]==ans[x2]*2)x2++;            if(ans[i]==ans[x3]*3)x3++;            if(ans[i]==ans[x5]*5)x5++;        }    int n;    while(cin>>n&&n!=0)        cout<<ans[n-1]<<endl;    return 0;}