264 - Ugly Number II

Problem

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.

Code

public class Solution {
    
    public int nthUglyNumber(int n) {
        int[] ans = new int[n];
        ans[0] = 1;
        int index2 = 0, index3 = 0, index5 = 0;
        for (int i = 1; i < n; ++i) {
            int t2 = ans[index2] * 2;
            int t3 = ans[index3] * 3;
            int t5 = ans[index5] * 5;
            int t = this.min(t2, t3, t5);
            if (t2 == t) {
                index2++;
            }
            if (t3 == t) {
                index3++;
            }
            if (t5 == t) {
                index5++;
            }
            ans[i] = t;
        }
        return ans[n - 1];
    }
    
    int min(int a, int b, int c) {
        return this.min(a, this.min(b, c));
    }
    
    int min(int a, int b) {
        return a < b ? a : b;
    }
    
}

Link: https://leetcode.com/problems/ugly-number-ii/