[Swift]LeetCode371. 两整数之和 | Sum of Two Integers

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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.

---

不使用运算符 + 和 - ​​​​​​​，计算两整数 ​​​​​​​a 、b ​​​​​​​之和。

示例 1:

输入: a = 1, b = 2
输出: 3

示例 2:

输入: a = -2, b = 3
输出: 1

---

8ms

class Solution {
    func getSum(_ a: Int, _ b: Int) -> Int {
        //按位取异或
        var res:Int = a^b
        //判断是否需要进位
        var forward = (a&b) << 1
        if forward != 0
        {
            //如有进位，则将二进制数左移一位，进行递归
            return getSum(res, forward)
        }
        return res
    }
}

---

8ms

class Solution {
    func getSum(_ a: Int, _ b: Int) -> Int {
        if a == 0 {
            return b
        }

        if b == 0 {
            return a
        }

        var a = a
        var b = b
        while b != 0 {
            let carry = a & b
            a = a ^ b
            b = carry << 1
        }
        return a
    }
}

---

8ms

class Solution {
    func getSum(_ a: Int, _ b: Int) -> Int {
        if a&b==0 {
            return a|b
        }
        return getSum(a^b, (a&b)<<1)
    }
}

---

12ms

class Solution {
    func getSum(_ a: Int, _ b: Int) -> Int {
        var carry = (a & b) << 1
    var result = a ^ b
    while carry != 0 {
      let carryTemp = carry
      carry  = (result & carryTemp) << 1
      result = result ^ carryTemp
    }
    return result
    }
}

---

16ms

class Solution {
    func getSum(_ a: Int, _ b: Int) -> Int {
        
        if b == 0 {
            return a
        } else {
            return getSum(a ^ b, (a & b) << 1)
        }
    }
}