剑指 Offer 58 - I. 翻转单词顺序

最容易想到的方法，用空格分割字符串成一个数组，swift的这个方法 直接把分割出来有空格的去掉了
再根据数组逆序来组装字符串

  func reverseWords(_ s: String) -> String {

      let array = s.split(separator:" ")
      let tempStr = array.reversed().joined(separator:" ")
      return tempStr
    }

另外的解法

func reverseWords(_ s: String) -> String {
 
        let length = s.count
        if length <= 0 {
            return s
        }
        var array = Array(s)
        //先要消除多余空格
        //像是开头是空格的情况
        var space = true
        var cur = 0
        for i in 0..<length {
            if array[i] != " " {
                array[cur] = array[i]
                cur += 1
                space = false
            }else {
                //第一次经历空格
                if space == false {
                    space = true
                    array[cur] = " "
                    cur += 1
                }
            }
        }
        //有效长度
        let len = space ? (cur - 1) : cur
        if len <= 0 {
            return ""
        }
        //去除多余部分
        array.removeSubrange(len..<length)
        reverseWord(&array,  0, len)
        //开始逆序单词
        //先寻找单词位置
        var preIndex = -1
        for i in 0..<len {
            if array[i] == " "{
                reverseWord(&array, preIndex + 1, i)
                preIndex = i
            }
            
        }
        //翻转最后一个单词
        reverseWord(&array,  preIndex + 1, len)

      return String(array)

    }
    func reverseWord( _ array:inout Array<Character>,_ start:Int ,_ length:Int) {
    
          var left = start ,right = length - 1
            while left < right {
              let temp = array[left]
              array[left] = array[right]
              array[right] = temp
              left += 1
              right -= 1
            }
    }