Group Anagrams

June 10, 2020

Here is a pretty common problem I came up on while doing LeetCode challenges.

Given an array of strings, group anagrams together.

Example: 

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

Note:

- All inputs will be in lowercase.
- The order of your output does not matter.

So first off, I wanted to collect the words which contain the same letters seperately, so in order to do that I created an Object.

let object = {}

Next, I wanted to iterate through my input array and see if any words had the same letters, In order to do so I split then sorted the letters to create the word in alphabetical order.

    strs.forEach(string => {
        let letters = string.split("").sort()
    })

Once the words are alphabetized, I can see if there is a key with the organized letters. If yes, I can add the original word to that key, if not, I create a new key-value pair, with the key being the organized letters and the value being the original.

Note that since each group of letters has its own array, when creating the key-value pair, the value must be an array.

 strs.forEach(string => {
       let letters = string.split("").sort()
         if(object[letters]) {
           object[letters].push(string)
       } else {
           object[letters] = [string]
       }
   })

Now you have all the anagrams grouped in an object.

{
  "a,e,t": ["eat","tea","ate"],
  "a,n,t": ["tan","nat"],
  "a,b,t": ["bat"]
}

Now our problem doesn’t care for objects but wants the ouput to be an array, so I used Object.keys and then the map method in order to turn it back into an array

    const keys = Object.keys(object)
    const values = keys.map(value => object[value])

Now all together using a ternary operator instead of an if else to make it cleaner.

const strs = ["eat", "tea", "tan", "ate", "nat", "bat"]
var groupAnagrams = function(strs) {
    let object = {}
    strs.forEach(string => {
        let letters = string.split("").sort()
        object[letters] ? object[letters].push(string) : object[letters] = [string]
    }) 
    const keys = Object.keys(object)
    const values = keys.map(value => object[value])
    return values
}
Output: 
[
  ["eat","tea","ate"],
  ["tan","nat"],
  ["bat"]
]

Hope this was of some help, and enjoy coding!