题解 | #进制转换#

import java.util.Scanner;
import java.util.Stack;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        char[] hexChars = in.nextLine().toUpperCase().toCharArray();
        Stack<Character> bucket = new Stack<>();
        int result = 0;

        for (int i = 2; i < hexChars.length; i++) {
            // 从最大位开始压栈
            bucket.push(hexChars[i]);
        }
	  
        // 开始弹栈，并累计数量，我们需要一个16^0, 16^1, 16^2...的计数器
        int unit = 1;
        while (!bucket.isEmpty()) {
            result += unit * getDec(bucket.pop());
            unit *= 16;
        }

        System.out.println(result);
    }

  	// 此部分使用switch遍历，用Map也可，总之代码量在这里很大
    private static int getDec(char hex) {
        int dec;
        switch (hex) {
            case '0' :
                dec = 0;
                break;
            case '1' :
                dec = 1;
                break;
            case '2' :
                dec = 2;
                break;
            case '3' :
                dec = 3;
                break;
            case '4' :
                dec = 4;
                break;
            case '5' :
                dec = 5;
                break;
            case '6' :
                dec = 6;
                break;
            case '7' :
                dec = 7;
                break;
            case '8' :
                dec = 8;
                break;
            case '9' :
                dec = 9;
                break;
            case 'A' :
                dec = 10;
                break;
            case 'B' :
                dec = 11;
                break;
            case 'C' :
                dec = 12;
                break;
            case 'D' :
                dec = 13;
                break;
            case 'E' :
                dec = 14;
                break;
            case 'F' :
                dec = 15;
                break;
            default :
                dec = -1;
        }
        return dec;
    }
}