Group Anagrams

 

1. Clarify the problem: Before diving into solving the problem, let's clarify the requirements:

  • We are given an array of strings.
  • We need to group the anagrams together and return them as a list of lists.
  • An anagram is a word or phrase formed by rearranging the letters of another word or phrase using all the original letters exactly once.

2. Analyze the problem: To solve this problem, we can use a hashmap to group the anagrams together. We iterate through the array of strings, sort each string, and use the sorted string as a key in the hashmap. The values of the hashmap will be lists of anagrams. Finally, we return the values of the hashmap as the grouped anagrams.

3. Design an algorithm: Here is the algorithm to group anagrams:

  1. Create an empty hashmap anagram_groups.
  2. Iterate through the array of strings:
    • Sort the current string and use it as a key in the anagram_groups hashmap.
    • If the key doesn't exist in the hashmap, initialize it with an empty list as the value.
    • Append the current string to the list of values corresponding to the key.
  3. Return the values of the anagram_groups hashmap as the grouped anagrams.

4. Explain your approach: The approach involves using a hashmap to group the anagrams together. We iterate through the array of strings and sort each string. The sorted string serves as the key in the hashmap, and we add the original string to the list of values corresponding to the key. This way, all the anagrams are grouped together.

5. Write clean and readable code:

python
def groupAnagrams(strs):
    anagram_groups = {}

    for word in strs:
        sorted_word = ''.join(sorted(word))

        if sorted_word not in anagram_groups:
            anagram_groups[sorted_word] = []

        anagram_groups[sorted_word].append(word)

    return list(anagram_groups.values())

6. Test your code:

python
# Test case 1
strs1 = ["eat", "tea", "tan", "ate", "nat", "bat"]
# The anagrams ["eat", "tea", "ate"] are grouped together.
# The anagrams ["tan", "nat"] are grouped together.
# The string "bat" doesn't have any anagrams.
# The output is [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]].
print(groupAnagrams(strs1))  # Expected output: [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]]

# Test case 2
strs2 = ["a"]
# The string "a" doesn't have any anagrams.
# The output is [["a"]].
print(groupAnagrams(strs2))  # Expected output: [["a"]]

# Test case 3
strs3 = []
# There are no strings in the input.
# The output is an empty list [].
print(groupAnagrams(strs3))  # Expected output: []

# Add more test cases to validate the solution

7. Optimize if necessary: The provided solution is already efficient with a time complexity of O(N * K * log(K)), where N is the number of strings in the input array and K is the average length of the strings. The space complexity is O(N) since we are using a hashmap to store the anagram groups. There is no further optimization possible for this problem.

8. Handle error cases: The code assumes that the input is a valid list of strings. If the input is not a list or if it contains elements that are not strings, the code may raise an exception or produce incorrect results. To handle such cases, we can add input validation at the beginning of the function to ensure the input is of the correct format.

9. Discuss complexity analysis: The time complexity of the solution is O(N * K * log(K)), where N is the number of strings in the input array and K is the average length of the strings. This complexity arises from iterating through the array of strings and sorting each string. The space complexity is O(N) since we store the anagram groups in a hashmap. The solution has an optimal time and space complexity given the problem requirements.

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