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
思路: 采用半加法的思想, 即两个二进制数单独的位相加其结果可以用异或运算得到，进位可以用与运算得到。
例子2+3，相当于10+11
1.10^11=01，carry=(10&11)<<1=100
2.001^100=101，carry(001&100)<<1=0
3.因为carry已经为0，不产生进位，此时的异或运算即为加法的结果101
递归版本
`
class Solution {
public int getSum(int a, int b) {
if(b==0)return a;
int carry=(a&b)<<1;
int sum=a^b;
return getSum(sum,carry);
}
}
`
循环版本
`
class Solution {
public int getSum(int a, int b) {
while (b!=0){
int carry=(a&b)<<1;
a=a^b;
b=carry;
}
return a;
}
}
`