[Swift]LeetCode231. 2的幂 | Power of Two

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Given an integer, write a function to determine if it is a power of two.

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

---

给定一个整数，编写一个函数来判断它是否是 2 的幂次方。

示例 1:

输入: 1
输出: true
解释: 20 = 1

示例 2:

输入: 16
输出: true
解释: 24 = 16

示例 3:

输入: 218
输出: false

---

12ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        for i in 0..<32 {
            if n == 1 << i {
                return true
            }
        }
        
        return false
    }
}

---

12ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        if n <= 0 { return false }
        if n == 1 { return true }
        var current = n
        while current > 2 {
            if current % 2 != 0 {
                return false
            } else {
                current = current / 2
            }
        }
        return true
    }
}

---

16ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        guard n > 0 else { return false }
        return String(n, radix: 2).filter { $0 == "1" }.count == 1
    }
}

---

20ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        if (n <= 0) {
            return false
        }
        var rencontre = false
        for digit in String(n, radix: 2) {
            if (digit == "1") {
                if rencontre {
                    return false
                } else {
                    rencontre = true
                }
            }
        }
        
        return true
    }
}

---

20ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        
        guard n > 0 else {
            return false
        }
        
        var num = n
        
        while num != 0 {
            
            if num == 1 || num == 2 {
                return true
            }
            
            if num % 2 != 0 {
                return false
            }
            
            num /= 2
        }
        
        return true
        
    }
}

---

24ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        if (n == 0) {
            return false;
        }
        return n & (n-1) == 0
    }
}

---

32ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        var number:Int = n;
        if number != 0 && number > 0 {
            if number == 1 || number == 2{
                return true;
            }
            while (number%2 == 0) {
                if (number == 2) {
                    break;
                }
                number = number / 2;
            }
            if (number % 2 == 0) {
                return true;
            }
        }
        return false;
    }
}

---

48ms

class Solution {
    func isPowerOfTwo(_ n: Int) -> Bool {
        if n <= 0 {
            return false
        }
        return 1<<32 % n == 0
    }
}