题目:给定两个字符串，确定其中一个字符串重新排列之后，是否能变成另外一个字符串.

核心代码:
<pre><code>` func permutation(strA:String,strB:String) -> Bool {

    if strA.characters.count != strB.characters.count {
        return false
    }
    
    var arr:[Int] = [Int].init(repeating: 0, count: 256)
    
    for i in 0..<strA.characters.count {
        
        let temp:String = strA[i] as String
        
        let index:Int = temp.toInt()
        
        arr[index] = arr[index] + 1
    }
    
    for i in 0..<strB.characters.count {
        let temp:String = strA[i] as String
        
        let index:Int = temp.toInt()
        
        if arr[index] - 1 < 0 {
            return false
        }
    }
    
    return true
}`<code></pre>

测试代码:
<pre><code>var strA:String = "student" var strB:String = "FlyElephant" var perResult:Bool = myString.permutation(strA: strA, strB: strB) print("\(strA)与\(strB)是不是变位词\(perResult)")</code></pre>