/*
  1.  for each char in s1 find the longest string in s2
  2.  compare it with previous string and replace if longer than the old String
*/

//  'AGGTAB', 'GXTXAYB' = 'GTAB'

function getTheLongestString(s1, s2, longestString = '', startingIndex = 0) {

  let tempLongestString = '';

  if(s1.length > 0) {

    [...s1].map((char) => {

      let s2Index = s2.indexOf(char, startingIndex);

      if(s2Index > -1) {
        startingIndex = s2Index + 1;
        tempLongestString += char;
      }

    });

    longestString = (tempLongestString.length > longestString.length) ? tempLongestString : longestString;

    return getTheLongestString(s1.substr(1), s2, longestString);


  } else return longestString;

}

console.log(getTheLongestString('ABAZDC', 'BACBAD'));
console.log(getTheLongestString('AGGTAB', 'GXTXAYB'));
console.log(getTheLongestString('aaaa', 'aa'));
console.log(getTheLongestString('ABBA', 'ABCABA'));

/*
  ABAZDC, BACBAD = ABAD
  AGGTAB, GXTXAYB = GTAB
  aaaa, aa = aa
*/