[Swift]LeetCode320. 通用简写 $ Generalized Abbreviation

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Write a function to generate the generalized abbreviations of a word.

Example:

Given word = "word", return the following list (order does not matter):

["word", "1ord", "w1rd", "wo1d", "wor1", "2rd", "w2d", "wo2", "1o1d", "1or1", "w1r1", "1o2", "2r1", "3d", "w3", "4"]

---

编写一个函数来生成一个单词的广义缩写。

例子：

给定word = "word",返回以下列表（顺序不重要）：

["word", "1ord", "w1rd", "wo1d", "wor1", "2rd", "w2d", "wo2", "1o1d", "1or1", "w1r1", "1o2", "2r1", "3d", "w3", "4"]

---

Solution:

class Solution {
    func generateAbbreviations(_ word:String) -> [String] {
        var res:[String] = [String]()
        var str:String = String()
        if !word.isEmpty
        {
            str = String(word.count)
        }
        res.append(str)
        for i in 0..<word.count
        {
            let arr:[String] = generateAbbreviations(word.subString(i + 1))
            for a in arr
            {
                var left:String = String()
                if i > 0
                {
                    left = String(i)
                }
                res.append(left + word.subString(i, 1) + a )
            }
        }
        return res        
    }
}

extension String {
    // 截取字符串：从index到结束处
    // - Parameter index: 开始索引
    // - Returns: 子字符串
    func subString(_ index: Int) -> String {
        let theIndex = self.index(self.endIndex, offsetBy: index - self.count)
        return String(self[theIndex..<endIndex])
    }
    
    // 截取字符串：指定索引和字符数
    // - begin: 开始截取处索引
    // - count: 截取的字符数量
    func subString(_ begin:Int,_ count:Int) -> String {
        let start = self.index(self.startIndex, offsetBy: max(0, begin))
        let end = self.index(self.startIndex, offsetBy:  min(self.count, begin + count))
        return String(self[start..<end]) 
    }
}

点击：Playground测试

var sol = Solution()
print(sol.generateAbbreviations("word"))
//Print ["4", "w3", "wo2", "wor1", "word", "wo1d", "w1r1", "w1rd", "w2d", "1o2", "1or1", "1ord", "1o1d", "2r1", "2rd", "3d"]