Sum of Two Integers

Problem

Given two integers a and b, return the sum of the two integers without using the + and - operators.

Examples

Example 1:

Input: a = 1, b = 1

Output: 2

Example 2:

Input: a = 4, b = 7

Output: 11

Constraints

• -1000 <= a, b <= 1000

You should aim for a solution with O(1) time and O(1) space.

Solution

Bit-wise adding.

class Solution {
public:
    int getSum(int a, int b) {
        int res = 0;
        int carry = 0;
        for (int i = 0; i < 32; ++i) {
            int a_bit = (a >> i) & 1;
            int b_bit = (b >> i) & 1;
            int res_bit = a_bit ^ b_bit ^ carry;
            carry = (a_bit + b_bit + carry) >= 2 ? 1 : 0;
            res |= (res_bit << i);
        }
        // Limit to 32 bits
        if (res > 0x7FFFFFFF) {
            res = ~(res ^ 0x7FFFFFFF);
        }
        return res;
    }
};