Add 'Longest Substring Without Repeating Characters'

Author: nickolashkraus

README.md

@@ -40,6 +40,8 @@ A collection of LeetCode solutions
 
 [Longest Increasing Subsequence](./src/longest_increasing_subsequence.py)
 
+[Longest Substring Without Repeating Characters](./src/test_longest_substring_without_repeating_characters.py)
+
 [Lowest Common Ancestor of a Binary Search Tree](./src/lowest_common_ancestor_of_a_binary_search_tree.py)
 
 [Lowest Common Ancestor of a Binary Tree](./src/lowest_common_ancestor_of_a_binary_tree.py)

src/longest_substring_without_repeating_characters.py

@@ -0,0 +1,54 @@
+"""
+3. Longest Substring Without Repeating Characters
+
+https://leetcode.com/problems/longest-substring-without-repeating-characters
+
+NOTES
+  * Use a sliding window.
+
+A subarray is a contiguous, non-empty sequence of elements within an array.
+Here, we just apply the canonical subarray/substring solution using a sliding
+window. Additionally, I've added a slightly more efficient solution that jumps
+the left pointer to the index after the last occurrence of the duplicate
+character.
+"""
+
+from collections import Counter
+
+
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        left, right, maximum_size = 0, 0, 0
+
+        # Maintain a mapping of character -> index of last occurrence.
+        d: dict[str, int] = {}
+
+        while right < len(s):
+            # Whenever we find a duplicate character, left is updated to the
+            # index after the last occurrence of that character.
+            if s[right] in d and d[s[right]] >= left:
+                left = d[s[right]] + 1
+            d[s[right]] = right
+            maximum_size = max(maximum_size, right - left + 1)
+            right += 1
+
+        return maximum_size
+
+
+class CanonicalSolution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        left, right, maximum_size = 0, 0, 0
+
+        # Maintain a mapping of character -> frequency.
+        counter: Counter[str] = Counter()
+
+        while right < len(s):
+            counter[s[right]] += 1
+            # Invariant: left <= right and substring has duplicate.
+            while left <= right and counter[s[right]] > 1:
+                counter[s[left]] -= 1
+                left += 1
+            maximum_size = max(maximum_size, right - left + 1)
+            right += 1
+
+        return maximum_size

tests/test_longest_substring_without_repeating_characters.py

@@ -0,0 +1,53 @@
+"""
+3. Longest Substring Without Repeating Characters
+
+https://leetcode.com/problems/longest-substring-without-repeating-characters
+"""
+
+from unittest import TestCase
+
+from src.longest_substring_without_repeating_characters import Solution, CanonicalSolution
+
+
+class TestSolution(TestCase):
+    def test_1(self):
+        exp = 3
+        assert Solution().lengthOfLongestSubstring("abcabcbb") == exp
+
+    def test_2(self):
+        exp = 1
+        assert Solution().lengthOfLongestSubstring("bbbbb") == exp
+
+    def test_3(self):
+        exp = 3
+        assert Solution().lengthOfLongestSubstring("pwwkew") == exp
+
+    def test_4(self):
+        exp = 1
+        assert Solution().lengthOfLongestSubstring(" ") == exp
+
+    def test_5(self):
+        exp = 2
+        assert Solution().lengthOfLongestSubstring("abba") == exp
+
+
+class TestCanonicalSolution(TestCase):
+    def test_1(self):
+        exp = 3
+        assert CanonicalSolution().lengthOfLongestSubstring("abcabcbb") == exp
+
+    def test_2(self):
+        exp = 1
+        assert CanonicalSolution().lengthOfLongestSubstring("bbbbb") == exp
+
+    def test_3(self):
+        exp = 3
+        assert CanonicalSolution().lengthOfLongestSubstring("pwwkew") == exp
+
+    def test_4(self):
+        exp = 1
+        assert CanonicalSolution().lengthOfLongestSubstring(" ") == exp
+
+    def test_5(self):
+        exp = 2
+        assert CanonicalSolution().lengthOfLongestSubstring("abba") == exp