找出一个数字是否以 2 开头的更快方法? [英] Faster way to find out if a number starts with 2?

问题描述

在 Java 中 - 查找给定整数是否以数字 2 开头而无需将数字转换为字符串的更快方法是什么?

In Java - what is the faster way to find if the given integer number is starting with the digit 2 without having to convert the number into a string?

String.valueOf(number).charAt(0) == '2'

推荐答案

如果您想避免将其转换为字符串，您可以继续除以 10 以找到最高有效数字:

If you wanted to avoid converting it to a string, you could just keep dividing by 10 to find the most significant digit:

int getMostSignificantDigit(int x)
{
    // Need to handle Integer.MIN_VALUE "specially" as the absolute value can't
    // represented. We can hard-code the fact that it starts with 2 :)
    x = x == Integer.MIN_VALUE ? 2 : Math.abs(x);
    while (x >= 10)
    {
        x = x / 10;
    }
    return x;
}

我不知道这是否会比 Husman 的 log/pow 方法更快.

I don't know whether this would be faster than Husman's log/pow approach.

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