Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -
用异或算不带进位的和，用与算进位
class Solution {
public:
int getSum(int a, int b) {
if (b == 0) return a;
int sum = a ^ b;
int carry = (a & b) << 1;
return getSum(sum, carry);
}
};
