题解 | #进制转换#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String hex = in.nextLine();
        //去掉0x前缀
        hex = hex.substring(2);
        int decimal = hexToDecimal(hex);
        System.out.println(decimal);
    }

    public static int hexToDecimal(String hex) {
        int decimal = 0;
        int len = hex.length();
        for (int i = 0; i < len; i++) {
            char hexChar = hex.charAt(len - 1 - i);
            //将每一个十六进制字段转成十进制后，乘以16的i次方
            decimal += hexCharToDecimal(hexChar) * (int) Math.pow(16, i);
        }
        return decimal;
    }

    public static int hexCharToDecimal(char hexChar) {
        if (hexChar >= '0' && hexChar <= '9') {
            return hexChar - '0';
        } else if (hexChar >= 'A' && hexChar <= 'F') {
            return hexChar - 'A' + 10;
        } else if (hexChar >= 'a' && hexChar <= 'f') {
            return hexChar - 'a' + 10;
        } else {
            throw new IllegalArgumentException("Invalid hex character: " + hexChar);
        }
    }
}