题解 | #进制转换#

import java.util.HashMap;
import java.util.Map;
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);
        in.useDelimiter("\n");

        Map<String, Integer> radix = new HashMap<String, Integer>() {{
            put("A", 10);
            put("B", 11);
            put("C", 12);
            put("D", 13);
            put("E", 14);
            put("F", 15);
        }};
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            String s = in.next();
            char[] chars = s.toCharArray();
            int result = 0;

            for (int i = chars.length - 1; i >= 2; i--) {
                char c = chars[i];
                int bit = chars.length - i;
                int bitNum = 1;
                for (int j = 1; j <= bit - 1; j++) {
                    bitNum *= 16;
                }
                result += bitNum * (radix.get(c + "") == null ? Integer.parseInt(c + "") : radix.get(c + ""));
            }
            System.out.println(result);
        }
    }
}