freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/longest-common-subsequence.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5e6dd1278e6ca105cde40ea9	Longest common subsequence	5	385271	longest-common-subsequence

--description--

The longest common subsequence (or LCS) of groups A and B is the longest group of elements from A and B that are common between the two groups and in the same order in each group. For example, the sequences "1234" and "1224533324" have an LCS of "1234":

1234

1224533324

For a string example, consider the sequences "thisisatest" and "testing123testing". An LCS would be "tsitest":

thisisatest

testing123testing.

Your code only needs to deal with strings.

For more information on this problem please see Wikipedia.

--instructions--

Write a case-sensitive function that returns the LCS of two strings. You don't need to show multiple LCS's.

--hints--

lcs should be a function.

assert(typeof lcs == 'function');

lcs("thisisatest", "testing123testing") should return a string.

assert(typeof lcs('thisisatest', 'testing123testing') == 'string');

lcs("thisisatest", "testing123testing") should return "tsitest".

assert.equal(lcs('thisisatest', 'testing123testing'), 'tsitest');

lcs("ABCDGH", "AEDFHR") should return "ADH".

assert.equal(lcs('ABCDGH', 'AEDFHR'), 'ADH');

lcs("AGGTAB", "GXTXAYB") should return "GTAB".

assert.equal(lcs('AGGTAB', 'GXTXAYB'), 'GTAB');

lcs("BDACDB", "BDCB") should return "BDCB".

assert.equal(lcs('BDACDB', 'BDCB'), 'BDCB');

lcs("ABAZDC", "BACBAD") should return "ABAD".

assert.equal(lcs('ABAZDC', 'BACBAD'), 'ABAD');

--seed--

--seed-contents--

function lcs(a, b) {

}

--solutions--

function lcs(a, b) {
  var aSub = a.substr(0, a.length - 1);
  var bSub = b.substr(0, b.length - 1);

  if (a.length === 0 || b.length === 0) {
    return '';
  } else if (a.charAt(a.length - 1) === b.charAt(b.length - 1)) {
    return lcs(aSub, bSub) + a.charAt(a.length - 1);
  } else {
    var x = lcs(a, bSub);
    var y = lcs(aSub, b);
    return (x.length > y.length) ? x : y;
  }
}