freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69cfca90e8a0a6d4d6871c54.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69cfca90e8a0a6d4d6871c54	Challenge 270: Longest Common Substring	28	challenge-270

--description--

Given a string, return the longest substring that appears more than once.

• The substrings can overlap.

--hints--

getLongestSubstring("abracadabra") should return "abra".

assert.equal(getLongestSubstring("abracadabra"), "abra");

getLongestSubstring("hello world hello") should return "hello".

assert.equal(getLongestSubstring("hello world hello"), "hello");

getLongestSubstring("mississippi") should return "issi".

assert.equal(getLongestSubstring("mississippi"), "issi");

getLongestSubstring("ha ha ha ha ha ha ha") should return "ha ha ha ha ha ha".

assert.equal(getLongestSubstring("ha ha ha ha ha ha ha"), "ha ha ha ha ha ha");

getLongestSubstring("the quick brown fox jumped over the lazy dog that the quick brown fox jumped over") should return "the quick brown fox jumped over".

assert.equal(getLongestSubstring("the quick brown fox jumped over the lazy dog that the quick brown fox jumped over"), "the quick brown fox jumped over");

--seed--

--seed-contents--

function getLongestSubstring(str) {

  return str;
}

--solutions--

function getLongestSubstring(str) {
  let longest = '';

  for (let len = str.length - 1; len >= 1; len--) {
    for (let i = 0; i <= str.length - len; i++) {
      const sub = str.slice(i, i + len);
      if (str.indexOf(sub) !== str.lastIndexOf(sub)) {
        return sub;
      }
    }
  }

  return longest;
}