[Swift]LeetCode869. 重新排序得到 2 的幂 | Reordered Power of 2

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Starting with a positive integer N, we reorder the digits in any order (including the original order) such that the leading digit is not zero.

Return true if and only if we can do this in a way such that the resulting number is a power of 2. 

Example 1:

Input: 1
Output: true

Example 2:

Input: 10
Output: false

Example 3:

Input: 16
Output: true

Example 4:

Input: 24
Output: false

Example 5:

Input: 46
Output: true 

Note:

1. 1 <= N <= 10^9

---

从正整数 N 开始，我们按任何顺序（包括原始顺序）将数字重新排序，注意其前导数字不能为零。

如果我们可以通过上述方式得到 2 的幂，返回 true；否则，返回 false。 

示例 1：

输入：1
输出：true

示例 2：

输入：10
输出：false

示例 3：

输入：16
输出：true

示例 4：

输入：24
输出：false

示例 5：

输入：46
输出：true 

提示：

1. 1 <= N <= 10^9

---

Runtime: 8 ms

Memory Usage: 18.6 MB

class Solution {
    func reorderedPowerOf2(_ N: Int) -> Bool {
        var c:Int = counter(N)
        for i in 0..<32
        {
            if counter(1 << i) == c
            {
                return true
            }
        }
        return false
    }

    func counter(_ N:Int) ->Int
    {
        var N = N
        var res:Int = 0
        while(N > 0)
        {
            res += Int(pow(10, Double(N % 10)))
            N /= 10
        }
        return res
    }
}

---

12ms

class Solution {
    func reorderedPowerOf2(_ N: Int) -> Bool {
         let a = count(N);
        for i in 0...31 {
            if a.elementsEqual(count(1 << i)) {
                return true;
            }
        }
      return false;
}
    
    func count(_ N: Int) -> [Int] {
        var n = N
        var ans =  [Int](repeating: 0, count: 31)
        while (n > 0) {
            let indx = n % 10;
            ans[indx] = ans[indx] + 1;
            n /= 10;
        }
        return ans
    }
}

---

16ms

class Solution {

    let pows2 = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912]
    var dictArr = [Int: [[Character: Int]]]()

    init() {
        for n in pows2 {
            let s = String(n)
            let val = toStringDict(n)
            if let arr = dictArr[s.count] {
                var varArr = arr
                varArr.append(val)
                dictArr[s.count] = varArr
            } else {
                dictArr[s.count] = [val]
            }
        }
    }

    func reorderedPowerOf2(_ N: Int) -> Bool {
        return dictArr[String(N).count]?.contains(toStringDict(N)) ?? false
    }

    func toStringDict(_ n: Int) -> [Character : Int] {
        let s = String(n)
        var dict: [Character : Int] = [:]
        for char in s.characters {
            if let val = dict[char] {
                dict[char] = val + 1
            } else {
                dict[char] = 1
            }
        }
        return dict
    }
}

---

28ms

class Solution {
    func reorderedPowerOf2(_ N: Int) -> Bool {
    if N == 1 {return true}
    var set = [String]()
    let stirng = String("\(N)".sorted(by: >))
    let max = Int(stirng)!
    for i in 1... {
        let number = 1 << i
        if number > max {break}
        set.append(String("\(number)".sorted(by: >)))
    }
     return set.contains(stirng)
    }
}