Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.

Example:
Given a = 1 and b = 2, return 3.

public class Solution {
    public int getSum(int a, int b) {
         int result = a ^ b; // 按位加
         int carray = (a & b) << 1; // 计算进位
         if(carray!=0) return  getSum(result,carray); //判断进位与处理
         return result;
    }
}