Add solution for longest substring without repeating characters

This commit introduces an implementation for finding the length of the longest substring without repeating characters using the sliding window technique. Includes a unit test to verify correctness with example test cases.

Author: nicholasadamou

Sliding Window/longest_substring_without_repeating_characters.py

@@ -0,0 +1,29 @@
+# https://neetcode.io/problems/longest-substring-without-duplicates
+
+import unittest
+
+def length_of_longest_substring(s: str) -> int:
+    seen = set()
+    left = 0
+    result = 0
+
+    for right, char in enumerate(s):
+        # Continuously remove leftmost characters from seen and move
+        # the left pointer forward whenever a duplicate is encountered
+
+        while char in seen:
+            seen.remove(s[left]) # Remove the leftmost character
+            left += 1 # Shrink the window until the duplicate is removed
+            continue
+
+        seen.add(char)
+
+        # Update the result with the current size of the window
+        result = max(result, right - left + 1)
+
+    return result
+
+class Test(unittest.TestCase):
+    def test_length_of_longest_substring(self):
+        self.assertEqual(length_of_longest_substring("zxyzxyz"), 3)
+        self.assertEqual(length_of_longest_substring("xxxx"), 1)