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);
        // 注意 hasNext 和 hasNextLine 的区别
        String hex = in.next().substring(2);

        int dec = 0;
        for(int i = 0;i < hex.length();i++) {
            int j = hex.length() - 1 - i;
            
            dec += hex2dec(hex.charAt(j)) * Math.pow(16,i);

        }
        System.out.println(dec);
        
    }

    public static int hex2dec(char x) {
        int num;
        switch (x) {
            case 'A': num = 10 ;break;
            case 'B': num = 11 ;break;
            case 'C': num = 12 ;break;
            case 'D': num = 13 ;break;
            case 'E': num = 14 ;break;
            case 'F': num = 15 ;break;
            default: num = Integer.valueOf(String.valueOf(x));
        }
        return num;
    }
}