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Swift Coding Challenges: Find longest prefix

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In the book Swift Coding Challenges, Chapter 12: Find longest prefix, the challenge is to "Write a function that accepts a string of words with a similar prefix, separated by spaces, and returns the longest substring that prefixes all words.

The book provided the following solution:

func challenge12(input: String) -> String {
    let parts = input.components(separatedBy: " ")
    guard let first = parts.first else { return "" }

    var currentPrefix = ""
    var bestPrefix = ""

    for letter in first {
    currentPrefix.append(letter)

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

        bestPrefix = currentPrefix
    }

    return bestPrefix
}

I chose another approach. Could you offer critique on my approach compared with the given solution? Thanks !

func challenge12(input: String) -> String {

    var words = input.components(separatedBy: " ")
    words.sort(){$0.count < $1.count}
    var prefix = words[0]
    for i in 1..<words.count {
        prefix = prefix.commonPrefix(with: words[i])
        guard prefix.count > 0 else {return ""}
    }
    return prefix
}
print(challenge12(input: "swift switch swill swim"))
print(challenge12(input: "flip flap flop"))
assert(challenge12(input: "swift switch swill swim") == "swi", "failed test")
assert(challenge12(input: "flip flap flop") == "fl", "failed test")

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