public int longestLength3(String s1, String s2, String s3)

Given THREE strings, return the length of the longer one.

  int len1 = s1.length();
  int len2 = s2.length();
  int len3 = s3.length();
  int longest = len1; // default, assume s1 is longer
  if (len2 > longest) { // test whether s2 is longer
    longest = len2;
  }
  if (len3 > longest) { // test whether s3 is longer
    longest = len3;
  }
  return longest;