diff --git a/src/my_project/interviews/google_top_exercises/round_1/09_longest_substring_without_repeating_characters.py b/src/my_project/interviews/google_top_exercises/round_1/09_longest_substring_without_repeating_characters.py
new file mode 100644
index 00000000..26efb51b
--- /dev/null
+++ b/src/my_project/interviews/google_top_exercises/round_1/09_longest_substring_without_repeating_characters.py
@@ -0,0 +1,21 @@
+from typing import List  
+
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        char_index = {}
+        left = 0
+        max_length = 0
+        
+        for right in range(len(s)):
+            # If character seen before and in current window
+            if s[right] in char_index and char_index[s[right]] >= left:
+                # Move left pointer past the last occurrence
+                left = char_index[s[right]] + 1
+            
+            # Update last seen index of current character
+            char_index[s[right]] = right
+            
+            # Update max length
+            max_length = max(max_length, right - left + 1)
+        
+        return max_length
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