题目:输入一个英文句子，翻转句子中单词的顺序，但单词内字符的顺序不变。为简单起见，标点符号和普通字母一样处理。例如输入字符串"I am a student."，则输出"student. a am I".
核心代码:
<pre><code>`

func reversePosition(strArr:inout [Character],begin:Int,end:Int)  {
    var low:Int = begin
    var high:Int = end
    while low < high {
        swap(&strArr[low], &strArr[high])
        low += 1
        high -= 1
    }
}

func reverseSentence(str:String) -> String {
    var strArr:[Character] = [Character]()
    for c in str.characters {
        strArr.append(c)
    }
    reversePosition(strArr: &strArr, begin: 0, end: str.characters.count - 1)
    
    var start:Int = 0
    var end:Int = 0
    
    
    while end < strArr.count {
        if String(strArr[start]) == " " {
            start += 1
            end += 1
        } else if String(strArr[end]) == " " {
             reversePosition(strArr: &strArr, begin: start, end: end-1)
             start = end
        } else {
            end += 1
        }
    }
    
    return String(strArr)
    
}`</code></pre>

测试代码:
<pre><code>var orginalStr:String = "I am FlyElephant" var reverseString:ReverseString = ReverseString() var reverseResult:String = reverseString.reverseSentence(str: orginalStr) print("反转之后的字符串---\(reverseResult)---")</code></pre>