Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.

Example:
Given a = 1 and b = 2, return 3.

Credits:
Special thanks to @fujiaozhu for adding this problem and creating all test cases.

不使用運算符 + 和 - ???????，計算兩整數 ???????a 、b ???????之和。

示例 1:

輸入: a = 1, b = 2
輸出: 3

示例 2:

輸入: a = -2, b = 3
輸出: 1

8ms

 1 class Solution {
 2     func getSum(_ a: Int, _ b: Int) -> Int {
 3         //按位取異或
 4         var res:Int = a^b
 5         //判斷是否需要進位
 6         var forward = (a&b) << 1
 7         if forward != 0
 8         {
 9             //如有進位，則將二進制數左移一位，進行遞歸
 

10             return getSum(res, forward)
11         }
12         return res
13     }
14 }

8ms

 1 class Solution {
 2     func getSum(_ a: Int, _ b: Int) -> Int {
 3         if a == 0 {
 4             return b
 5         }
 6 
 7         if b == 0 {
 8             return a
 9         }
 
10 
11         var a = a
12         var b = b
13         while b != 0 {
14             let carry = a & b
15             a = a ^ b
16             b = carry << 1
17         }
18         return a
19     }
20 }

8ms

1 class Solution {
2     func getSum(_ a: Int, _ b: Int) -> Int {
3         if a&b==0 {
4             return a|b
5         }
6         return getSum(a^b, (a&b)<<1)
7     }
8 }

12ms

 1 class Solution {
 2     func getSum(_ a: Int, _ b: Int) -> Int {
 3         var carry = (a & b) << 1
 4     var result = a ^ b
 5     while carry != 0 {
 6       let carryTemp = carry
 7       carry  = (result & carryTemp) << 1
 8       result = result ^ carryTemp
 9     }
10     return result
11     }
12 }

16ms

 1 class Solution {
 2     func getSum(_ a: Int, _ b: Int) -> Int {
 3         
 4         if b == 0 {
 5             return a
 6         } else {
 7             return getSum(a ^ b, (a & b) << 1)
 8         }
 9     }
10 }

[Swift]LeetCode371. 兩整數之和 | Sum of Two Integers