LeetCode Problem 49: Group Anagrams

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.

Solution: This problem can be solved in 4 steps.

Step 1: Create a result map of type<String, List>.

Step 2: Iterate over each string in input, convert it to an array, sort it and then convert it back to String.

Step 3: Now check if result.containsKey(key) in result map then result.get(key).add(input str) else, result.put(key, new ArrayList()).

Step 4: return new ArrayList(result.values())

class Solution {
 public List<List<String>> groupAnagrams(String[] strs) {
   if (strs.length == 0) return new ArrayList();
   Map<String, List> ans = new HashMap<String, List>();
 
   for (String s : strs) {
          char[] ca = s.toCharArray();
          Arrays.sort(ca);
          String key = String.valueOf(ca);
          
          if (!ans.containsKey(key)) ans.put(key, new ArrayList());
          ans.get(key).add(s);
    }
   return new ArrayList(ans.values());
 }
}