Question

How to find the longest common prefix of all the words in a string with Swift

Answer 1

import Foundation

func longestCommonPrefix(_ input: String) -> String {
    let trimmed = input.trimmingCharacters(in: .whitespacesAndNewlines)
    if trimmed.isEmpty { return "" }

    // Split by non‑word characters (similar to Java's split("\\W+"))
    let words = trimmed
        .lowercased()
        .components(separatedBy: CharacterSet.alphanumerics.inverted)
        .filter { !$0.isEmpty }

    guard let first = words.first else { return "" }

    var prefix = first

    for word in words {
        while !word.hasPrefix(prefix) {
            prefix.removeLast()
            if prefix.isEmpty { return "" }
        }
    }

    return prefix
}

let s1 = "The lowly inhabitants of the lowland were surprised to see the lower branches."
print("LCP: '\(longestCommonPrefix(s1))'")

let s2 = "unclear, uncertain, unexpected"
print("LCP: '\(longestCommonPrefix(s2))'")



/*
run:

LCP: ''
LCP: 'un'

*/

 

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