Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.
Example 1:
Input: a = 1, b = 2
Output: 3
Example 2:
Input: a = -2, b = 3
Output: 1
不让用加减，就是用逻辑计算了，异或（^）等于不考虑进位后的加减，与（&）等于只保留进位的结果，那最终结果就是（不进位结果 + 进位结果<<1）
不让用+，则可以用递归解决不得不的+
func getSum(a int, b int) int {
if b == 0 {
return a
}
return getSum(a ^ b, (a & b) << 1)
}