Java 代码

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import static java.lang.System.*;

public class Main{

    public static int cmp(int[] a, int[] b){
        if(a.length > b.length) return 1;
        if(a.length < b.length) return -1;
        for(int i = a.length -1; i>=0; i--){
            if(a[i] > b[i]) return 1;
            else if (a[i] < b[i]) return -1;
        }
        return 0;
    }

    public static void main(String[] agrs) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        String m = br.readLine(), n = br.readLine();
        int al = m.length(), bl = n.length(), len = Math.max(al, bl);
        int[] a = new int[al];
        int[] b = new int[bl];
        int[] c = new int[len];
        for(int i = al -1, j = 0; i >= 0; i--,j++) a[j] = m.charAt(i) - '0';
        for(int i = bl -1, j = 0; i >= 0; i--,j++) b[j] = n.charAt(i) - '0';

        int p = cmp(a,b);
        if( p == -1){
            int[] tmp = b;
            b = a;
            a = tmp;
        }else if(p == 0){
            out.print('0');
            return;
        }

        for(int i = 0, t = 0; i < len; i++, t = t < 0 ? 1 : 0){
            t = a[i] - t;
            if( i < b.length) t -= b[i];
            c[i] = (t + 10) % 10;
        }
        //排除多余的0
        while(--len > 0 && c[len] == 0);
        if(p == -1) out.print('-');
        for(int i = len; i >= 0; i--) out.print(c[i]);
    }
}