For strings "ABCD", "ABEF" and "ACEF", the LCP is "A"

For strings "ABCDEFG", "ABCEFG" and "ABCEFA", the LCP is "ABC"

public String longestCommonPrefix(String[] strs) {
    if (strs == null || strs.length == 0) {
        return "";
    }
    String lcp = strs[0];
    for (int i = 1; i < strs.length; i++) {
        lcp = getLCP(lcp, strs[i]);
    }
    return lcp;
}

public String getLCP(String s1, String s2) {
    StringBuilder sb = new StringBuilder();
    int n = Math.min(s1.length(), s2. length());
    for (int i = 0; i < n; i++) {
        if (s1.charAt(i) == s2.charAt(i)) {
            sb.append(s1.charAt(i));
        } else {
            break;
        }
    }
    return sb.toString();
}