题解 | #进制转换2#

import java.util.*;
import java.math.BigInteger;



// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {

    public static final int BASE_A = 65;
    public static final int BASE_a = 97;

    public static BigInteger parse_to_decimal(String num, String base) {
        int n = num.length();
        BigInteger ret = new BigInteger("0");
        BigInteger basic = new BigInteger(base);
        for (int i = 0; i < n; i++) {
            char cur = num.charAt(i);
            BigInteger factor;
            if (Character.isDigit(cur)) {
                factor = new BigInteger(cur + "");
            } else {
                factor = new BigInteger(10 + (cur - BASE_A) + "");
            }
            ret = ret.add(factor.multiply(basic.pow(n - i - 1)));
        }
        return ret;
    }

    public static String parse_to_NDecimal(BigInteger num, String d) {
        if (num.equals(new BigInteger("0"))) return "0";
        StringBuilder sb = new StringBuilder();
        BigInteger base = new BigInteger(d);
        while (!num.equals(new BigInteger("0"))) {
            int bit = num.mod(base).intValue();
            sb.append(bit > 9 ? (char)(bit - 10 + BASE_a) : bit);
            num = num.divide(base);
        }
        return sb.reverse().toString();
    }


    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String M = in.next();
        String N = in.next();
        in.nextLine();
        String X = in.next();
        System.out.println(parse_to_NDecimal(parse_to_decimal(X, M), N));
    }
}