---
title: 'LeetCode 371. Sum of Two Integers'
disqus: hackmd
---

# LeetCode 371. Sum of Two Integers

## Description

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

## Example

Input: a = 1, b = 2
Output: 3

Input: a = 2, b = 3
Output: 5

## Constraints

-1000 <= a, b <= 1000

## Answer

此題可用bit operation來實現，以加法器的概念來實作，取XOR為疊加，取AND為須進位項，以迴圈來循環操作到不需進位為止。

// 2022_04_05
int getSum(int a, int b){
    int and = 0, xor = 0;
    while(a&b){
        // 轉成unsigned int 可以容納32位，如此才能計算左移一位，
        // 轉回int為最高位導致變回符號位，
        and = ((unsigned int)(a&b)) << 1;
        xor = a ^ b;
        a = and;
        b = xor;
    }
    return a | b;
}

## Link
https://leetcode.com/problems/sum-of-two-integers/
###### tags: `Leetcode`