[Swift]LeetCode171. Excel表列序号 | Excel Sheet Column Number

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Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 
    ...

Example 1:

Input: "A"
Output: 1

Example 2:

Input: "AB"
Output: 28

Example 3:

Input: "ZY"
Output: 701

---

class Solution {
    func titleToNumber(_ s: String) -> Int {
        //26进制转10进制
        var n:Int = s.count
        var res:Int = 0
        var temp:Int = 1
        // A:65 Z:90
        for m in (0..<n).reversed()
        {
            var letter = s[s.index(s.startIndex,offsetBy:m)]
            var num:Int = Int()
            //使用for-in循环遍历转化成String的letter
            for scalar in String(letter).unicodeScalars
            {
                num = Int(scalar.value)
            }
            //num - 65 + 1
            res += (num - 64) * temp
            temp *= 26 
        }
        return res
    }
}

---

24ms

class Solution {
            func titleToNumber(_ s : String) -> Int {

    var i  = 0
            var result = 0
            
            for char in s.unicodeScalars{
result+=(Int(char.value)-64)*self.canWinNim2(n: (s.count-1-i))
                
                i+=1
            }
               return result
        }
    func canWinNim2( n: Int) -> Int{
        var count = n
        var  ret=1
        while count>0 {
            ret =  self.canWinNim1(ret)
            count-=1
        }
       
        return ret
       
    }
    func canWinNim1(_ n: Int) -> Int{
        return n*26
    }
}

---

16ms

class Solution {
    func titleToNumber(_ s: String) -> Int {
  
      var columnNumber = 0
      let offset = 64   
       
      for letter in s.utf8 { 
        columnNumber = columnNumber * 26 + Int(letter) - offset
      }   
      
      return columnNumber
    } 
}

---

20ms

class Solution {
    func titleToNumber(_ s: String) -> Int {
        
        var s = Array(s)
        var result = 0
        for c in s {
            let num = getNumber(c)
            result = result * 26 + num
        }
        
        return result
    }
    
    func getNumber(_ c: Character) -> Int {
        return Int(c.unicodeScalars.first!.value - "A".unicodeScalars.first!.value) + 1
    }
    
}