mMximumSwap.swift

func maximumSwap(number: Int) {
    if number == 0 {
        return
    }
  
    var digits = digitsFromNum(num: number)
    var max_index = 0
    var left = 0
    var right = 0
    
    for i in 0..<digits.count {
        if digits[i] > digits[max_index] {
            max_index = i
        } else if digits[i] < digits[max_index] {
            left = i
            right = max_index
        }
    }
    
    digits.swapAt(left, right)
   
    print(numFromDigits(digits))
}


func digitsFromNum(num: Int) -> [Int] {
    var digits = [Int]()
    var num = num
    
    while num != 0 {
        digits.append(num % 10)
        num /= 10
    }
    
    return digits
}


func numFromDigits(_ digits: [Int]) -> Int {
    var num = 0
    
    for i in 0..<digits.count {
        num += Int(pow(10, Double(i))) * digits[i]
    }
    
    return num
}

maximumSwap(number: 2736)