가장 긴 공통 접두사

fun longestCommonPrefix(strs: Array<String>): String {
    if (strs.isEmpty()) return ""
    strs.sort()
    val first = strs[0]
    val last = strs[strs.size - 1]
    var i = 0
    while (i < first.length && first[i] == last[i]) i++
    return first.substring(0, i)
}