华为2013机试题 大数相减JAVA实现

题目要求大概：

输入a,b两个大数，长度100以内，默认a>=b;不考虑其他情况；

例如：输入 1000000000000001

                      1

           输出   1000000000000000

import java.util.Scanner;

public class Main {
	public static String func(String a,String b) {
		int[] aa = new int[a.length()];
		int[] bb = new int[b.length()];
		for (int i = 0; i < a.length(); i++) {
			aa[i] = Integer.valueOf(String.valueOf(a.charat(i)));
		}
		for (int i = 0; i < b.length(); i++) {
			bb[i] = Integer.valueOf(String.valueOf(b.charat(i)));
		}
		int index = b.length();
		for (int i = a.length() - 1; i >= 0; i--) {
			if (index >= 1) {
				if (aa[i] >= bb[index - 1]) {
					aa[i] = aa[i] - bb[index - 1];
				} else {
					int temp = 1;
					while (aa[i - temp] == 0) {
						aa[i - temp] = 9;
						temp++;
					}
					aa[i - temp]--;
					aa[i] = aa[i] + 10 - bb[index - 1];
				}
				index--;
			}
		}
		int start = a.length()-1;
		for (int i = 0; i < a.length(); i++) {
			if (aa[i] != 0) {
				start = i;
				break;
			}
		}
		String result = "";
		for (int i = start; i < a.length(); i++) {
			result += aa[i];
		}
		return result;
	}

	public static void main(String[] args) {
		String a = "";
		String b = "";
		Scanner cin = new Scanner(system.in);
		while (cin.hasNext()) {
			if (a == "") {
				a = cin.nextLine();
			} else {
				b = cin.nextLine();
				System.out.println(func(a,b));
				a = "";
				b = "";
			}
		}
	}
}