Improve checking anagrams in O(n) with dictionary (#4806)

strings/check_anagrams.py

@@ -1,6 +1,7 @@
 """
 wiki: https://en.wikipedia.org/wiki/Anagram
 """
+from collections import defaultdict
 
 
 def check_anagrams(first_str: str, second_str: str) -> bool:
@@ -16,10 +17,30 @@ def check_anagrams(first_str: str, second_str: str) -> bool:
     >>> check_anagrams('There', 'Their')
     False
     """
-    return (
-        "".join(sorted(first_str.lower())).strip()
-        == "".join(sorted(second_str.lower())).strip()
-    )
+    first_str = first_str.lower().strip()
+    second_str = second_str.lower().strip()
+
+    # Remove whitespace
+    first_str = first_str.replace(" ", "")
+    second_str = second_str.replace(" ", "")
+
+    # Strings of different lengths are not anagrams
+    if len(first_str) != len(second_str):
+        return False
+
+    # Default values for count should be 0
+    count = defaultdict(int)
+
+    # For each character in input strings,
+    # increment count in the corresponding
+    for i in range(len(first_str)):
+        count[first_str[i]] += 1
+        count[second_str[i]] -= 1
+
+    for _count in count.values():
+        if _count != 0:
+            return False
+    return True
 
 
 if __name__ == "__main__":