swift 算法 简单5.最长公共前缀

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编写一个函数来查找字符串数组中的最长公共前缀。

如果不存在公共前缀，返回空字符串 ""。

示例 1:

输入: ["flower","flow","flight"]
输出: "fl"
示例 2:

输入: ["dog","racecar","car"]
输出: ""
解释: 输入不存在公共前缀。

解法：

  func longestCommonPrefix(_ strs: [String]) -> String {
        
        var strs = strs
        
        //1.遍历字符串数组中的每一个字符串
        //2.找出最短的字符串
        if(strs.count == 1){
            return strs[0]
        }
        
        for i in 0..<strs.count {
            for j in 0..<strs.count-i-1{
                if(strs[j].count>strs[j+1].count){
                    let temp = strs[j]
                    strs[j] = strs[j+1]
                    strs[j+1] = temp
                }
            }
        }
        //3.从最短的字符串中的第一个字符开始向所有的字符串第一个字符匹配。。。。不匹配则return “”
        var prxStr:String = ""
        //取最短的字符串 判断循环比较次数
        for indexlenth in 0..<strs[0].count {
            
            let str = strs[0]
            let index3 = str.index(str.startIndex, offsetBy: 0)
            let index4 = str.index(str.startIndex, offsetBy: indexlenth+1 > strs[0].count ? strs[0].count : indexlenth+1)
            let sub4 = str[index3..<index4]
            
            //与后面的字符串每一个字符比较
            for indexrow in 1..<strs.count {
                
                let str2 = strs[indexrow]
                let index5 = str2.index(str2.startIndex, offsetBy: 0)
                let index6 = str2.index(str2.startIndex, offsetBy: indexlenth+1 > strs[0].count ? strs[0].count : indexlenth+1)
                let sub7 = str2[index5..<index6]
                
                if sub4 == sub7 {
                    print("相同的值 \(sub4):\(sub7)")
                    prxStr = String(sub4)
                    
                }else{
                    
                    if(prxStr.isEmpty){
                        return ""
                    }else{
                        let index8 = prxStr.index(prxStr.startIndex, offsetBy: 0)
                        let index9 = prxStr.index(prxStr.startIndex, offsetBy: prxStr.count-1)
                        let prxStr = prxStr[index8..<index9]
                        
                        return String(prxStr)
                    }
                    
                }
            }
        }
        
        return prxStr
    }