Ugly number

题目描述

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

1
2
9
0

Sample Output

1
2
10
分析
每个丑数都是2^x*3^y*5^z组成的，对于输入的n,所以可以对小于n的丑数进行排序，得到第n个丑数。
C++代码

#include <iostream>
#include <iomanip>
#define min(x,y) ((x)<(y)?(x):(y))
using namespace std;

int a[1505];
int num ;
void init()
{
    int i1=1,i2=1,i3=1;
    a[1] = 1;
    int i ;
    i = 2;
    while(i <= 1500)
    {
        a[i] = min(min(a[i1] * 2 ,a[i2] * 3 ) ,a[i3] * 5 );
        while(a[i1] * 2 == a[i] ) i1 ++ ;
        while(a[i2] * 3 == a[i] ) i2 ++ ;
        while(a[i3] * 5 == a[i] ) i3 ++ ;
        i ++ ;
    }
}
int main()
{
    int n ;
    init();
    while(scanf("%d",&n)!=EOF && n != 0)
    {
        printf("%d\n",a[n]);
    }
    return 0;
}

时间复杂度不会分析。。。。求指导