Group Anagrams - Leetcode 49

Group Anagrams - Leetcode 49

Problem - Leetcode

Given an array of strings strs, group the anagrams together. You can return the answer in any order.

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

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


  • 1 <= strs.length <= 10<sup>4</sup>

  • 0 <= strs[i].length <= 100

  • strs[i] consists of lowercase English letters.

Answer-1 Top Runtime in Golang

func groupAnagrams(strs []string) [][]string {
    anagramMap := make(map[[26]int][]string)
    for _, s := range strs {
        var count [26]int
        for _, c := range s {
        anagramMap[count] = append(anagramMap[count], s)
    result := make([][]string, len(anagramMap))
    idx := 0
    for _, v := range anagramMap {
        result[idx] = v
    return result

The Go code step-by-step:

  1. The function groupAnagrams takes a slice of strings called strs as input and returns a 2D slice of strings where each inner slice represents a group of anagrams.

  2. Inside the function, an empty map named anagramMap is created. This map is used to store anagrams grouped by their character frequency patterns. The keys in this map are arrays of integers with length 26 (representing the count of each lowercase letter in the English alphabet) and the values are slices of strings containing anagrams with the same character frequency pattern.

  3. A loop iterates through each string s in the strs slice.

  4. Inside the loop, an array of integers named count with a length of 26 is created. This array will store the frequency of each lowercase letter in the current string s.

  5. Another loop iterates through each character c in the string s.

  6. For each character c, the frequency count for the corresponding lowercase letter is incremented in the count array. This is done by subtracting the ASCII value of 'a' from the character c, resulting in an index that corresponds to the position of the letter in the count array.

  7. After processing all the characters in the string s, the count array now holds the frequency of each letter in that string.

  8. The string s is appended to the slice of strings associated with the calculated count array in the anagramMap. This effectively groups strings with the same character frequency pattern together.

  9. The above steps are repeated for all strings in the input strs, populating the anagramMap map.

  10. After processing all input strings, a new 2D slice of strings named result is created, with a length equal to the number of unique character frequency patterns (i.e., the number of keys in anagramMap).

  11. A variable idx is initialized to 0. This variable will be used to fill in the result slice.

  12. A loop iterates through the values (which are slices of strings) in the anagramMap.

  13. For each value (slice of strings), the value is assigned to the result slice at the index idx.

  14. The idx variable is incremented to prepare for the next iteration.

  15. Once all values from the anagramMap have been assigned to the result slice, the result slice is populated with groups of anagrams.

  16. Finally, the function returns the populated result slice, where each inner slice represents a group of anagrams with the same character frequency pattern.

In summary, this code takes a list of strings, groups them based on their anagram patterns using a map, and returns a 2D slice containing these groups of anagrams.

Answer-2 Top Memory in Golang

func groupAnagrams(strs []string) [][]string {
    res := make([][]string, 0)
    for _, str := range strs {
        found := false
        for i, amalArr := range res {
            ele := amalArr[0]
            if isAnagram(ele, str) {
                amalArr = append(amalArr, str)   
                found = true
                res[i] = amalArr
        if !found {
            temparr := make([]string, 0)
            temparr = append(temparr, str)
            res = append(res, temparr)
    return res

func isAnagram(s string, t string) bool {
    arr := make([]int, 26)
    for _, c := range s {
        arr[byte(c)-byte('a')] += 1
    for _, c := range t {
        arr[byte(c)-byte('a')] -= 1
    for _, c := range arr {
       if c != 0 {
           return false
    return true


This code defines two functions: groupAnagrams and isAnagram. The main purpose of the code is to group anagrams together from a given slice of strings. Anagrams are words that have the same letters but in a different order.

  1. isAnagram(s string, t string) bool: This function takes two strings as input and checks whether they are anagrams. It does so by counting the occurrences of each character in both strings and comparing the character frequency arrays.

    • arr := make([]int, 26): Creates an integer array of size 26 to store the frequency of each lowercase English letter.

    • for _, c := range s: Loops through each character in the first input string s.

      • arr[byte(c)-byte('a')] += 1: Increments the count for the character's position in the array by 1.
    • for _, c := range t: Loops through each character in the second input string t.

      • arr[byte(c)-byte('a')] -= 1: Decrements the count for the character's position in the array by 1.
    • Finally, it checks whether all the counts in the arr are 0, indicating that both strings have the same character frequency.

      • If all counts are 0, it returns true (strings are anagrams), otherwise, it returns false.
  2. groupAnagrams(strs []string) [][]string: This function takes a slice of strings strs and groups anagrams together.

    • res := make([][]string, 0): Initializes an empty slice of slices of strings to store the grouped anagrams.

    • It then iterates through each string str in the input slice strs.

      • found := false: A flag to track whether the current string is found within existing anagram groups.

      • The loop then goes through the existing anagram groups stored in res and checks if the current str is an anagram with any of the strings in the group.

        • If an anagram is found, the current str is appended to that group, and found is set to true.

        • The modified group is then stored back into res.

      • If no anagram group is found for the current str, a new temporary array temparr is created, containing only the current str.

        • This temporary array is then appended to the res array.
    • After processing all input strings, the function returns the res array, containing the grouped anagram arrays.

Overall, the groupAnagrams function uses the isAnagram function to group anagrams together by iterating through the input strings and either adding them to existing groups or creating new groups as needed.

Did you find this article valuable?

Support Jyotirmoy Barman by becoming a sponsor. Any amount is appreciated!