Write a function that takes a list of strings and returns the longest string that is a prefix of at least two strings in the list. longestCommonPrefix(["flower","flow","flight"]) -> "fl" longestCommonPrefix(["dog","racecar","car"]) -> "" longestCommonPrefix(["interstellar","internet","internal","interval"]) -> "inte"

longest_common_prefix.gleam

import gleam/int
import gleam/io
import gleam/list
import gleam/string

pub fn chars_at_position(pos: Int, as_char: List(List(String))) {
  // given a position, create a list of characters
  list.map(as_char, fn(x) {
    case { list.last(list.take(x, pos)) } {
      Ok(val) -> val
      _ -> ""
    }
  })
}

pub fn build(as_char: List(List(String)), min_length: Int) {
  list.range(0, min_length)
  |> list.map(fn(pos) { chars_at_position(pos + 1, as_char) })
}

pub fn longest_common_prefix(items: List(String)) -> String {
  // convert the 1-d list into 2d list of characters
  let as_char = list.map(items, string.to_graphemes)
  // find the shortest length so that comparision can exit
  let min_length =
    list.map(as_char, list.length)
    |> list.fold(1_000_000_000, fn(x, y) { int.min(x, y) })

  let matches =
    //Get a list of the character at each position to compare later
    build(as_char, min_length)
    // compare the returned character at the each position
    |> list.filter(fn(x) { list.unique(x) |> list.length == 1 })
  // Build the prefix
  let prefix =
    list.map(matches, fn(x) {
      case { list.first(x) } {
        Ok(val) -> val
        _ -> ""
      }
    })
    |> string.join("")
  prefix
}

pub fn main() -> Nil {
  list.each(
    [
      ["flower", "flow", "flight"],
      ["dog", "racecar", "car"],
      ["interstellar", "internet", "internal", "interval"],
    ],
    fn(items) {
      echo items
      let prefix = longest_common_prefix(items)
      io.println(string.concat(["prefix:", " ", prefix]))
    },
  )
}

longest_common_prefix.py

"""
Write a function that takes a list of strings and returns the longest string 
that is a prefix of at least two strings in the list.

longestCommonPrefix(["flower","flow","flight"])
"fl"

longestCommonPrefix(["dog","racecar","car"])
""

longestCommonPrefix(["interstellar","internet","internal","interval"])
"inte"
"""
def longestCommonPrefix(items):
    if not items:
        return ""
    
    if len(items) == 1:
        return items[1]

    longest, i = "", 0
    prev = items[0][i]
    while True:
        prev, skip = items[0][i], False
        for item in items[1:]:
            if item[i] != prev:
                skip = True
                break
        else:
            longest += prev
            i += 1
        if skip:
            break
    return longest


print(longestCommonPrefix(["flower","flow","flight"]), "fl")
print(longestCommonPrefix(["dog","racecar","car"]), "")
print(longestCommonPrefix(["interstellar","internet","internal","interval"]), "inter")