题目:利用字符重复出现的次数，可以实现基本的字符串压缩功能.字符串串“aabcccccaaa”经压缩会变成“a2b1c5a3”,若压缩后的字符串没有变短，则返回原先的字符串.

核心代码:
<pre><code>` func compressBetter(str:String) -> String {

    let count:Int = str.characters.count
    
    if count == 0 {
        return ""
    }
    
    var result:String = ""
    
    var last:Character = str[0] as Character
    var charCount:Int = 0
    
    for i in 0..<count {
        
        let temp:Character = str[i] as Character
        
        if temp == last {
            charCount += 1
        } else {
            result.append(last)
            result.append("\(charCount)")
            last = temp
            charCount = 1
        }
    }
    
    result.append(last)
    result.append("\(charCount)")
    
    if result.characters.count >= count {
        return str
    }
    
    return result
}`</code></pre>

测试代码:
<pre><code>var compressString:String = "abbcccdddd" var compressResult:String = myString.compressBetter(str: compressString) print("压缩结果:\(compressResult)")</code></pre>