Good morning! Here's our prompt for today.

A very common interview challenge is to determine how often words appear in a given string or set of strings. Here's a version of this: return a list of duplicate words in a sentence.

For example, given 'The dog is the best', returns ["the"].

Likewise, given 'Happy thanksgiving, I am so full', you would return an empty array. This is because there are no duplicates in the string.

Constraints

• The total length of the string <= 100000
• The string will consist of ASCII characters (may be some or all)
• Expected time complexity : O(n) where n are the number of words in the string
• Expected space complexity : O(n)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

function findDuplicates(str) {

  const dupes = [];

  // fill in

​

  return dupes;

}

​

try {

  assert.deepEqual(findDuplicates('The dog is the best'), ['the']);

​

  console.log(

    'PASSED: ' + "`findDuplicates('The dog is the best')` returns `['the']`"

  );

} catch (err) {

  console.log(err);

}

​

try {

  assert.deepEqual(findDuplicates('Happy thanksgiving, I am so full'), []);

​

  console.log(

    'PASSED: ' +

      "`findDuplicates('Happy thanksgiving, I am so full’)` returns `[]`"

  );

} catch (err) {

  console.log(err);

}

Here's our guided, illustrated walk-through.

How do I use this guide?