Find longest common prefix?

Question

In two strings:

\"Mary Had a Little Lamb\"
\"Mary Had a Big Lamb\"

should return

\"Mary Had a \"

Answer 1

A very easy solution can be:

  public static String longestCommonPrefix(String[] strs) {
    if (strs.length == 0) {
        return "";
    }
    String result = strs[0];
    for (int i = 1; i < strs.length; i++) {
        while (!strs[i].startsWith(result)) {
            result = result.substring(0, result.length() - 1);
        }
    }
    return result;
}

Answer 2

You don't need to use a StringBuilder - just return the substring:

public String greatestCommonPrefix(String a, String b) {
    int minLength = Math.min(a.length(), b.length());
    for (int i = 0; i < minLength; i++) {
        if (a.charAt(i) != b.charAt(i)) {
            return a.substring(0, i);
        }
    }
    return a.substring(0, minLength);
}

Answer 3

This solution applied to a multiple string array. When you have 3 or 4 strings, it's better to use StringBuilder. For 2 strings, it's ok to use substring. Code in C#:

    public string LongestCommonPrefix(string[] strs) {
    if(strs.Length == 0) return string.Empty;

    Array.Sort(strs);

    var first = strs[0];
    var last = strs[strs.Length - 1];

    var sb = new StringBuilder();
    for(int i = 0; i< first.Length; i++)
    {
        if(first[i] != last[i])
        {
            break;
        }
        sb.Append(first[i]);
    }

    return sb.ToString();
}