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. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note that 1 is typically treated as an ugly number.

 

3 pointer index2, index3, index5

public class Solution {
    public int nthUglyNumber(int n) {
        int isUglyNum[] = new int[n];
        isUglyNum[0] = 1;
        int count = 1;
        int index2 = 0;
        int index3 = 0;
        int index5 = 0;
        while(count < n){
            isUglyNum[count] = Math.min(isUglyNum[index2] * 2, Math.min(isUglyNum[index3] * 3, isUglyNum[index5] * 5));
            if(isUglyNum[count] == isUglyNum[index2] * 2)
                index2 ++;
            if(isUglyNum[count] == isUglyNum[index3] * 3)
                index3 ++;
            if(isUglyNum[count] == isUglyNum[index5] * 5)
                index5 ++;
            count++;
        }
        return isUglyNum[n-1];
    }
    
}