[Swift]LeetCode476. 数字的补数 | Number Complement

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Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. You could assume no leading zero bit in the integer’s binary representation. 

Example 1:

Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2. 

Example 2:

Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

---

给定一个正整数，输出它的补数。补数是对该数的二进制表示取反。

注意:

1. 给定的整数保证在32位带符号整数的范围内。
2. 你可以假定二进制数不包含前导零位。

示例 1:

输入: 5
输出: 2
解释: 5的二进制表示为101（没有前导零位），其补数为010。所以你需要输出2。

示例 2:

输入: 1
输出: 0
解释: 1的二进制表示为1（没有前导零位），其补数为0。所以你需要输出0。

---

Runtime: 8 ms

Memory Usage: 3.8 MB

class Solution {
    func findComplement(_ num: Int) -> Int {
        return (1 - num % 2) + 2 * (num <= 1 ? 0 : findComplement(num / 2))
    }
}

---

Runtime: 8 ms

Memory Usage: 3.8 MB

class Solution {
    func findComplement(_ num: Int) -> Int {
        var mask:Int = Int.max
        while ((mask & num) != 0)
        {
            mask <<= 1
        }
        return ~mask & ~num
    }
}

---

8ms

class Solution {
    func findComplement(_ num: Int) -> Int {
    var numberOfBitsNeeded = 0
    var number = num
    while number > 0 {
        number /= 2
        numberOfBitsNeeded += 1
    }
    
    
    let allOnes = (2 << (numberOfBitsNeeded - 1)) - 1
    
    
    return (num ^ allOnes)
    }
}

---

3842 kb

class Solution {
    func findComplement(_ num: Int) -> Int {
        let numberOfBits = (String(num,radix:2)).count
        return ((1 << numberOfBits) - 1) ^ num
    }
}

---

3858 kb

class Solution {
    func findComplement(_ num: Int) -> Int {
        
        let bitCount = num.bitWidth - num.leadingZeroBitCount
        
        var mask = 1
        
        for _ in 0..<bitCount - 1 {
            mask = mask << 1 + 1
        }
        
        return num ^ mask
    }
}

---

16ms

class Solution {
    func findComplement(_ b: Int) -> Int {
        var count = 0
        var sum = 0
        while sum <= b {
            count += 1
            sum = 1 << count
        }
        
        let rtn = sum - 1 - b
        return rtn
    }
}

---

28ms

class Solution {
    func findComplement(_ num: Int) -> Int {
        var num = num
        var res = 0
        var offset = 0

        while num > 0 {
            res = res + ((num & 1) ^ 1) << offset
            num = num >> 1
            offset += 1
        }

        return res
    }
}