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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0264_ugly_number_ii;

// #Medium #Hash_Table #Dynamic_Programming #Math #Heap_Priority_Queue #Dynamic_Programming_I_Day_11
// #2022_07_05_Time_2_ms_(99.91%)_Space_41.3_MB_(91.38%)

/**
 * 264 - Ugly Number II\.
 *
 * Medium
 *
 * An **ugly number** is a positive integer whose prime factors are limited to `2`, `3`, and `5`.
 *
 * Given an integer `n`, return _the_ n^th _**ugly number**_.
 *
 * **Example 1:**
 *
 * **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. 
 *
 * **Example 2:**
 *
 * **Input:** n = 1
 *
 * **Output:** 1
 *
 * **Explanation:** 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5. 
 *
 * **Constraints:**
 *
 * *   `1 <= n <= 1690`
**/
public class Solution {
    public int nthUglyNumber(int n) {
        int[] ugly = new int[n];
        int i2 = 0;
        int i3 = 0;
        int i5 = 0;
        int ugly2 = 2;
        int ugly3 = 3;
        int ugly5 = 5;
        int nextugly;
        ugly[0] = 1;
        for (int i = 1; i < n; i++) {
            nextugly = Math.min(Math.min(ugly2, ugly3), ugly5);
            ugly[i] = nextugly;
            if (nextugly == ugly2) {
                i2++;
                ugly2 = ugly[i2] * 2;
            }
            if (nextugly == ugly3) {
                i3++;
                ugly3 = ugly[i3] * 3;
            }
            if (nextugly == ugly5) {
                i5++;
                ugly5 = ugly[i5] * 5;
            }
        }
        return ugly[n - 1];
    }
}