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Group Anagrams using HashMap

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Write a Java program to group anagrams together from an array of strings. 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. You need to return the anagrams grouped together in a list of lists.

Example 1
    

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

    • Step 1: Create a HashMap to store groups of anagrams with sorted strings as keys.
      • 

    • Step 2: For each string, sort its characters to create a key (e.g., "eat" becomes "aet").
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    • Step 3: Add the original string to the list mapped to its sorted key.
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    • Step 4: Group "eat", "tea", and "ate" together as they all sort to "aet".
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    • Step 5: Group "tan" and "nat" together as they both sort to "ant".
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    • Step 6: "bat" sorts to "abt" and forms its own group.
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    • Step 7: Return all the groups as a list of lists.
      • 

    •
Example 2
    

  • Input: strs = [""]
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  • Output: [[""]]
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  • Explanation: 
      

    • Step 1: Create a HashMap to store groups of anagrams.
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    • Step 2: For the empty string, its sorted form is also an empty string.
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    • Step 3: Add the empty string to the list mapped to the empty string key.
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    • Step 4: Return a list containing a single group with an empty string.
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    •
Constraints
    

  • 1 ≤ strs.length ≤ 10^4
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  • 0 ≤ strs[i].length ≤ 100
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  • strs[i] consists of lowercase English letters
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  • Time Complexity: O(n * k), where n is the length of strs and k is the maximum length of a string in strs
    • 

  • Space Complexity: O(n * k) for storing all strings
    •
StringsHash MapeBayPhillips
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Hint
Solution

Solution Hints

    
  
  • Use a HashMap where the key is a representation of the anagram and the value is a list of strings that are anagrams
    • 
  
  • For each string, create a sorted version to use as a key (since anagrams will have the same sorted string)
    • 
  
  • Alternatively, create a count of each character to use as a key
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  • Add each string to the appropriate list in the HashMap
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  • After processing all strings, return the values of the HashMap as a list of lists
    •

Steps to solve by this approach:

 Step 1: Create a HashMap where the key is the sorted version of a string and the value is a list of strings that are anagrams.

 Step 2: Iterate through each string in the input array.

 Step 3: Sort the characters of the current string to create a key for identifying anagrams.

 Step 4: If the sorted string is not already a key in the HashMap, create a new entry with an empty list.

 Step 5: Add the original string to the list associated with its sorted key.

 Step 6: After processing all strings, convert the HashMap values to a list of lists and return it.

 Step 7: This approach ensures that all anagrams are grouped together because they will have the same sorted string representation.

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