[Swift]LeetCode14. 最长公共前缀 | Longest Common Prefix

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Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

Example 1:

Input: ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Note:

All given inputs are in lowercase letters a-z.

---

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。

说明:

所有输入只包含小写字母 a-z 。

---

16ms

class Solution {
    func longestCommonPrefix(_ strs: [String]) -> String {
        let minStr = try? strs.min(by: { $0.count < $1.count })
        guard var minS = minStr! else {
            return ""
        }
        
        var endIndex = minS.endIndex
        for str in strs {
            if (str.hasPrefix(minS)) {
                continue
            }
            while endIndex > minS.startIndex && !str.hasPrefix(minS) {
                endIndex = minS.index(before: endIndex)
                minS = String(minS[minS.startIndex..<endIndex])
            }
        }
        return minS
    }
}

---

20ms

class Solution {
       func longestCommonPrefix(_ strs: [String]) -> String {
        
        if strs.count == 0 {
            return ""
        }
        var prefix = strs[0]
        for i in 0..<strs.count {
            while strs[i].hasPrefix(prefix) == false {
                prefix = prefix.substring(to: prefix.index(before: prefix.endIndex))
                if prefix.isEmpty {
                    return ""
                }
            }
        }
        return prefix
    }
}

---

24ms

class Solution {
    func longestCommonPrefix(_ strs: [String]) -> String {
        guard strs.count > 0 else { return "" }
        var shortestPrefix = strs.min{ $0.count < $1.count }!
        print(shortestPrefix)
        for s in strs {
            while shortestPrefix.count > 0 , !s.hasPrefix(shortestPrefix) {
                shortestPrefix.removeLast()
            }
        }
        return shortestPrefix
    }
}

---

28ms

class Solution {
    func longestCommonPrefix(_ strs: [String]) -> String {

        var res = ""
        if strs.isEmpty {
            
            return res
        }
        
        res = strs[0]
        
        for i in 1..<strs.count {
            
            var find = Array(strs[i])
            var current = Array(res)
            res = ""
            for i in 0..<find.count {
                
                if i >= current.count {
                    break
                }
                
                if current[i] != find[i] {
                    
                    break
                } else {
                    
                    res += String(current[i])
                }
            }
            
        }
        
        return res
    }
}

---

32ms

class Solution {
  func longestCommonPrefix(_ strs: [String]) -> String {
    guard let first = strs.first else { return "" }

    var currentPrefix = ""
    var bestPrefix = ""

    for letter in first { 
      currentPrefix.append(letter)

      for word in strs {
        if !word.hasPrefix(currentPrefix) { 
          return bestPrefix 
        }
      }

      bestPrefix = currentPrefix
    }

    return bestPrefix                
  }
}