JZ-033-Ugly number

Ugly number

Title description

The number that contains only prime factors 2, 3, and 5 is called Ugly Number. For example, 6 and 8 are both ugly numbers, but 14 is not because it contains the prime factor 7. Traditionally, we regard 1 as the first ugly number. Find the Nth ugly number in ascending order.

title link : ugly number

Code

/**
 * 标题：丑数
 * 题目描述
 * 把只包含质因子2、3和5的数称作丑数（Ugly Number）。例如6、8都是丑数，但14不是，因为它包含质因子7。 习惯上我们把1当做是第一个丑数。求按从小到大的顺序的第N个丑数。
 * 题目链接：
 * https://www.nowcoder.com/practice/6aa9e04fc3794f68acf8778237ba065b?tpId=13&&tqId=11186&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz33 {

    public int getUglyNumber_Solution(int index) {
        if (index <= 6) {
            return index;
        }
        int i2 = 0, i3 = 0, i5 = 0;
        int[] dp = new int[index];
        dp[0] = 1;
        for (int i = 1; i < index; i++) {
            int next2 = dp[i2] * 2, next3 = dp[i3] * 3, next5 = dp[i5] * 5;
            dp[i] = Math.min(next2, Math.min(next3, next5));
            if (dp[i] == next2) {
                i2++;
            }
            if (dp[i] == next3) {
                i3++;
            }
            if (dp[i] == next5) {
                i5++;
            }
        }
        return dp[index - 1];
    }

    public static void main(String[] args) {
        Jz33 jz33 = new Jz33();
        System.out.println(jz33.getUglyNumber_Solution(10));
    }
}

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