剑指offer-丑数

我们把只包含质因子 2、3 和 5 的数称作丑数（Ugly Number）。求按从小到大的顺序的第 n 个丑数。

相关链接：

力扣

public class NumberOfUgly {

    
    public int nthUglyNumber(int n) {
        int[] dp = new int[n];
        int xIndex = 0;
        int yIndex = 0;
        int zIndex = 0;
        dp[0] = 1;
        for (int i = 1; i < n; i++) {
            int xValue = dp[xIndex] * 2;
            int yValue = dp[yIndex] * 3;
            int zValue = dp[zIndex] * 5;
            dp[i] = Math.min(Math.min(xValue, yValue), zValue);
            if (xValue == dp[i]) {
                xIndex++;
            }
            if (yValue == dp[i]) {
                yIndex++;
            }
            if (zValue == dp[i]) {
                zIndex++;
            }
        }
        return dp[n-1];
    }

    
    private boolean isUgly(int num) {
        while (num % 2 == 0) {
            num = num / 2;
        }
        while (num % 5 == 0) {
            num = num / 5;
        }
        while (num % 3 == 0) {
            num = num / 3;
        }
        return num == 1;
    }

    public static void main(String[] args) {
        NumberOfUgly numberOfUgly = new NumberOfUgly();
        System.out.println(numberOfUgly.nthUglyNumber(10));
    }
}