[Swift]LeetCode670. 最大交换 | Maximum Swap

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Given a non-negative integer, you could swap two digits at most once to get the maximum valued number. Return the maximum valued number you could get.

Example 1:

Input: 2736
Output: 7236
Explanation: Swap the number 2 and the number 7. 

Example 2:

Input: 9973
Output: 9973
Explanation: No swap. 

Note:

1. The given number is in the range [0, 10^8]

---

给定一个非负整数，你至多可以交换一次数字中的任意两位。返回你能得到的最大值。

示例 1 :

输入: 2736
输出: 7236
解释: 交换数字2和数字7。

示例 2 :

输入: 9973
输出: 9973
解释: 不需要交换。

注意:

1. 给定数字的范围是 [0, 10^8]

---

Runtime: 8 ms

Memory Usage: 19 MB

class Solution {
    func maximumSwap(_ num: Int) -> Int {
        var arr:[Character] = Array(String(num))
        var res:Int = num
        var n:Int = arr.count
        var str:String = String()
        for i in 0..<n
        {
            for j in (i + 1)..<n
            {
                arr.swapAt(i,j)
                str = String(arr)
                res = max(res, Int(str) ?? 0)
                arr.swapAt(i,j)
            }
        }
        return res
    }
}

---

8ms

class Solution {
    func maximumSwap(_ num: Int) -> Int {
        let str = String(num)
        var arr = Array(str)
        var sortedNumbers = arr.sorted()
        sortedNumbers = sortedNumbers.reversed()
        
        var index = 0
        while index < arr.count - 1 && arr[index] == sortedNumbers[index]{            
            index += 1
        }
        if index >= arr.count - 1 {
            return num
        }
        let temp = arr[index]
        var indexNeedChanged = index
        for i in (index ..< arr.count).reversed() {
            if arr[i] == sortedNumbers[index] {
                indexNeedChanged = i
                break
            }
        }
        arr[index] = sortedNumbers[index]    
        arr[indexNeedChanged] = temp
        let ns = String(arr)
        return Int(ns)!
    }
}

---

20ms

class Solution {
    func maximumSwap(_ num: Int) -> Int {
        var nums = [String]()
        for char in "\(num)" {
            nums.append(char.description)
        }
        
        let count = nums.count
        for i in 0..<count - 1 {
            var mark = count - 1
            for j in (i + 1..<count).reversed() {
                if nums[j] > nums[mark] {
                    mark = j
                }
            }
            print(i)
            print(mark)
            if nums[mark] > nums[i] {
                let temp = nums[i]
                nums[i] = nums[mark]
                nums[mark] = temp
                return Int(nums.joined()) ?? 0
            }
        }
        return num
    }
}

---

24ms

class Solution {
    func maximumSwap(_ num: Int) -> Int {
        var num = num
        var nums: [Int] = []
        
        while num > 0 {
            nums.append(num % 10)
            num /= 10
        }
        
        for n in stride(from: nums.count-1, to: -1, by: -1) {
            var mx = nums[0]
            var idx = 0
            for k in 0..<n {
                if nums[k] > mx {
                    mx = nums[k]
                    idx = k
                }
            }
            if mx > nums[n] {
                nums.swapAt(idx, n)
                break
            }
        }
        
        var res = 0
        for n in nums.reversed() {
            res = res * 10 + n
        }
        
        return res
    }
}