LeetCode-in-All

49. Group Anagrams

Medium

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.

Example 1:

Input: strs = [“eat”,”tea”,”tan”,”ate”,”nat”,”bat”]

Output: [[“bat”],[“nat”,”tan”],[“ate”,”eat”,”tea”]]

Example 2:

Input: strs = [””]

Output: [[””]]

Example 3:

Input: strs = [“a”]

Output: [[“a”]]

Constraints:

• 1 <= strs.length <= 104
• 0 <= strs[i].length <= 100
• strs[i] consists of lowercase English letters.

To solve the “Group Anagrams” problem in Swift with the Solution class, follow these steps:

1. Define a method groupAnagrams in the Solution class that takes an array of strings strs as input and returns a list of lists of strings.
2. Initialize an empty HashMap to store the groups of anagrams. The key will be the sorted string, and the value will be a list of strings.
3. Iterate through each string str in the input array strs.
4. Sort the characters of the current string str to create a key for the HashMap.
5. Check if the sorted string exists as a key in the HashMap:
   • If it does, add the original string str to the corresponding list of strings.
   • If it doesn’t, create a new entry in the HashMap with the sorted string as the key and a new list containing str as the value.
6. After iterating through all strings, return the values of the HashMap as the result.

Here’s the implementation of the groupAnagrams method in Swift:

public class Solution {
    public func groupAnagrams(_ strs: [String]) -> [[String]] {
        var hm = [String: [String]]()
        for s in strs {
            let sortedStr = String(s.sorted())
            if hm[sortedStr] == nil {
                hm[sortedStr] = [String]()
            }
            hm[sortedStr]!.append(s)
        }
        return Array(hm.values)
    }
}

This implementation ensures that all anagrams are grouped together efficiently using a HashMap.

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