add: group anagrams

data_structures/neetcode_150/src/GroupAnagrams.java

@@ -0,0 +1,47 @@
+package neetcode_150.src;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Given an array of strings `strs`, group the anagrams together.
+ * You can return the answer in any order.
+ */
+public class GroupAnagrams {
+    public static void main(String[] args) {
+        System.out.println("\nGroup Anagrams ==> ");
+        String[] strs = { "eat", "tea", "tan", "ate", "nat", "bat" };
+        List<List<String>> ans = groupAnagrams(strs);
+        System.out.println(ans);
+    }
+
+    private static List<List<String>> groupAnagrams(String[] strs) {
+        if (strs.length == 0) {
+            return new ArrayList<>();
+        }
+
+        Map<String, List<String>> ansMap = new HashMap<>();
+        int[] count = new int[26];
+
+        for (String s : strs) {
+            Arrays.fill(count, 0);
+            for (char c : s.toCharArray()) {
+                count[c - 'a']++;
+            }
+
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < 26; i++) {
+                sb.append("#").append(count[i]);
+            }
+            String key = sb.toString();
+
+            ansMap.putIfAbsent(key, new ArrayList<>());
+            ansMap.get(key).add(s);
+        }
+
+        return new ArrayList<>(ansMap.values());
+    }
+}