Ugly Number II

 Ugly Number II

Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. 

Example:

Input: n = 10
Output: 12
Explanation: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note:  

1. 1 is typically treated as an ugly number.
2. n does not exceed 1690.

class Solution {

public:

    

    

    int nthUglyNumber(int n) {

      int a[n];

        a[0]=1;

        int ind2=0,ind3=0,ind5=0;

        

        for(int i=1;i<n;++i)

        {

              a[i]=min(a[ind2]*2,min(a[ind3]*3,a[ind5]*5));

            if(a[i]==(a[ind2]*2))++ind2;

            if(a[i]==a[ind3]*3)++ind3;

            if(a[i]==a[ind5]*5)++ind5;

          

        }

        return a[n-1];

     

    }

};