Create 3. Longest Substring Without Repeating Characters.md

競技プロ就活部PR用/3. Longest Substring Without Repeating Characters.md

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+## Sliding Window(set)による解法 ★
+---
+### 1回目 (3m20s)
+時間計算量: O(N)<br>
+空間計算量: O(N)
+
+```python
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        left = 0
+        max_length = 0
+        letters_in_windows = set()
+
+        for right in range(len(s)):
+            while s[right] in letters_in_windows:
+                letters_in_windows.discard(s[left])
+                left += 1
+
+            letters_in_windows.add(s[right])
+
+            max_length = max(max_length, right - left + 1)
+
+        return max_length
+```
+
+## dictを使った解法 
+---
+時間計算量: O(N)<br>
+空間計算量: O(N)
+
+(あまり旨みはない。indexが必要な時に便利か。)
+```python
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        left = 0
+        letter_to_index = defaultdict(int)
+        max_length = 0
+
+        for right in range(len(s)):
+            while letter_to_index[s[right]] > 0:
+                letter_to_index[s[left]] -= 1
+                left += 1
+
+            letter_to_index[s[right]] += 1
+            max_length = max(max_length, right - left + 1)
+
+        return max_length
+```
+
+## dictを使った解法 (indexを記録)
+---
+時間計算量: O(N)<br>
+空間計算量: O(N)
+```python
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        left = 0
+        letter_to_index = defaultdict(int)
+        max_length = 0
+
+        for right in range(len(s)):
+            if s[right] in letter_to_index and left <= letter_to_index[s[right]]:
+                left = letter_to_index[s[right]] + 1
+
+            letter_to_index[s[right]] = right
+            max_length = max(max_length, right - left + 1)
+
+        return max_length
+```