Find longest common prefix string in an array - (swift implementation, slicing method)

prefix.swift

func longestCommonPrefix(_ strs: [String]) -> String {
    // base case
    if strs.isEmpty {
        return ""
    }
    
    if var prefixStr = strs.first {
        
        for index in 1..<strs.count {
            let str = strs[index]
            while str.contains(prefixStr) == false {
                let index = prefixStr.index(prefixStr.startIndex, offsetBy: prefixStr.count - 1)
                prefixStr = String(prefixStr[..<index])
                if prefixStr.count == 0 {
                    return ""
                }
            }
        }
        return prefixStr
    }
    
    return ""
}

longestCommonPrefix(["flower", "florida", "flow"])

will be failed in case like ["c","acc","ccc"]

If the first word is too long and the other words are short, then your code ends up with character count of the first word iterations of while loop.

Example: ["abcdefgijklmnopqrstuvwxyz", "b"]

---

My version.

// LC: https://leetcode.com/problems/longest-common-prefix

// TC -> O(min(strs) * n)
// SC -> O(str.first!.count)

func longestCommonPrefix(_ strs: [String]) -> String {
    
    if strs.count == 1 {
        return strs.first!
    }
    
    guard let temp = strs.first, !temp.isEmpty else {
        return ""
    }
    
    var endIndex: String.Index? = nil
    
    outerLoop: 
    for index in temp.indices {
            for str in strs {
    
                if str.isEmpty {
                    return ""
                }
    
                // checking index out of range and characters equality
                if index >= str.endIndex || str[index] != temp[index] {
                    break outerLoop
                }
            }
            endIndex = index
        }
    
    if let endIndex {
        return String(temp[...endIndex])
    }
    
    return ""
}