3. 大数相减

import java.util.Scanner;

public class Main {

    public static void main(String args[]) {
        Scanner scan = new Scanner(System.in);
        String line;
        while (scan.hasNext()) {
            line = scan.nextLine().trim();
            String[] strs = line.split("-");
            char[] cha1 = strs[0].toCharArray();
            char[] cha2 = strs[1].toCharArray();
            int len1 = cha1.length;
            int len2 = cha2.length;
            for (int i = len2 - 1,j = len1 - 1; i >= 0; i--,j--) {
                int a = cha1[j] - 48;
                int b = cha2[i] - 48;
                if (a < b) {
                    if (j > 0) {
                        a += 10 - b;
                        cha1[j - 1] -= 1; 
                    } else {
                        a -= b;
                    }
                } else {
                    a -= b;
                }
                cha1[j] = (char) (a + 48);
            }
            boolean flag = true;
            for (int i = 0; i < cha1.length; i++) {
                if (cha1[i] == '0' && flag) {
                    continue;
                } else {
                    flag = false;
                }
                System.out.print(cha1[i]);
            }
        }
    }
}