Algorithm 202 (My Interview Question): Grouping Anagrams in 3 Ways

Last year, I had a technical interview and one of the questions was on Anagrams. I solved the problem in 3 ways today and I want to share it with you in a moment.

Question:

Given an array of strings, group anagrams together.

Anagram: These are words that are made up of the same letters but in different orders.

Example:
Input: ["eat", "tea", "tan", "ate", "nat", "bat"]

Output:
[
  ["ate","eat","tea"],
  ["nat","tan"],
  ["bat"]
]

If you have been following my Algorithm series, then you are well fortified for this challenge.

groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"]);

/*
  [ [ 'ate', 'eat', 'tea' ], [ 'nat', 'tan' ], [ 'bat' ] ]
*/

Prerequisite

1. String Reversal
2. Word Anagram
3. Sentence Anagram
4. Array Chunking
5. Array Merging Without Duplicates

Solution

• .map(), sort(), join(), Set(), forEach(), filter(), push, spread operator

      function groupAnagrams(array) {
        let finalArray = [];

        // rearrange each word to check for anagram
        let rearranged = array.map(element => {
          return [...element].sort().join("");
        });

        // remove duplicates
        let uniqueArray = [...new Set(rearranged)];

        // compare original array with dupliates
        uniqueArray.forEach(word => {
          let chunk = array.filter(char => word === [...char].sort().join(""));

          finalArray.push(chunk.sort());
        });

        return finalArray;
      }

• for...of...loop, sort(), join(), filter(), push, split(), indexOf()

      function groupAnagrams(array) {
        let finalArray = [];
        let rearranged = [];

        // rearrange each word to check for anagram
        for (element of array) {
          rearranged.push(
            element
              .split("")
              .sort()
              .join("")
          );
        }

        // remove duplicates
        let uniqueArray = rearranged.filter(
          (member, index) => rearranged.indexOf(member) === index
        );

        // compare original array with dupliates
        for (word of uniqueArray) {
          let chunk = [];

          for (char of array) {
            if (
              word ===
              char
                .split("")
                .sort()
                .join("")
            ) {
              chunk.push(char);
            }
          }
          finalArray.push(chunk.sort());
        }
        return finalArray;
      }

• for...loop, while...loop, sort(), join(), push(), split(), includes()

      function groupAnagrams(array) {
        let finalArray = [];
        let rearranged = [];

        // rearrange each word to check for anagram
        let i = 0;
        while (i < array.length) {
          rearranged.push(
            array[i]
              .split("")
              .sort()
              .join("")
          );
          i++;
        }

        // remove duplicates
        let uniqueArray = [];
        for (let j = 0; j <= rearranged.length; j++) {
          if (!uniqueArray.includes(rearranged[j])) {
            uniqueArray.push(rearranged[j]);
          }
        }

        // compare original array with dupliates
        let counter = 0;
        while (counter < uniqueArray.length) {
          let chunk = [];

          for (let k = 0; k < array.length; k++) {
            if (
              uniqueArray[counter] ===
              array[k]
                .split("")
                .sort()
                .join("")
            ) {
              chunk.push(array[k]);
            }
          }

          if (chunk.length != 0) {
            finalArray.push(chunk.sort());
          }
          counter++;
        }
        return finalArray;
      }

Conclusion

Interview questions like this one we just solved tends to test how far you have dived into algorithm. As you must have noted, the solution to just this problem is built upon other 5 algorithms we have solved in the past. So starting from the basics is very important.

There are many ways to solve problems programmatically. I will love to know other ways you solved yours in the comment section.

Up Next: Algorithm 101: 4 Ways to FizzBuzz a Single Number

If you have questions, comments or suggestions, please drop them in the comment section.

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Thank You For Your Time.

Comments

[Wojciech Rebis]

Great article, and good interview question.
Good work, keep it up! :)

Just wanted to share my approach to this:

function groupAnagrams(anagrams) {
  const wordGroups = anagrams.reduce((groups, anagram) => {
    const word = anagram.split('').sort().join('');
    if (groups[word]) {
      groups[word].push(anagram);
    } else {
      groups[word] = [anagram];
    }
    return groups;
  }, {});

  return Object.values(wordGroups).map(group => group);
} 

What do you think about it?

[NJOKU SAMSON EBERE]

Thank you Wojciech. I love your method. It's very clever and coincise. Works perfectly too.

dev-to-uploads.s3.amazonaws.com/i/...

Do you mind explaining what is going on in the reduce() function probably by commenting the code?

[Wojciech Rebis]

I thought of reducing array of anagrams to an object which keys will be initial words and values arrays of anagrams from these words.

[Ganesh Shetty]

Tried pretty much in the same way

function groupAnagrams(array) {
var reducedObject = array.reduce((acc, cur) => {
var newcur=cur.split('').sort().join('');
if (!acc[newcur]) {
acc[newcur] = [cur]
} else {
acc[newcur] = [...acc[newcur], cur]
}
return acc;
}, {});
return Object.values(reducedObject);
}
console.log(groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"]));

[Bruno Oliveira]

Nice! :)

[NJOKU SAMSON EBERE]

Bruno, Thank you for taking your time to read through!