[prograsshopper] week 7 solutions

longest-substring-without-repeating-characters/prograsshopper.py

@@ -0,0 +1,38 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        # sol 1
+        # time complexity: O(n^2) / memory complexity: O(n)
+        if len(s) in [0, 1]:
+            return len(s)
+
+        from collections import defaultdict
+        strings = []
+        for i in range(0, len(s) - 1):
+            char_dict = defaultdict(int)
+            char_dict[s[i]] += 1
+            for j in range(i + 1, len(s)):
+                char_dict[s[j]] += 1
+                if char_dict[s[j]] > 1:
+                    strings.append(s[i:j])
+                    break
+            else:
+                strings.append(s[i:])
+
+        max_len = len(strings[0])
+        for elem in strings:
+            max_len = max(max_len, len(elem))
+        return max_len
+
+        # sol 2
+        # time complexity: O(n) / memory complexity: O(n)
+        str_set = set()
+        left = 0
+        max_len = 0
+
+        for right in range(len(s)):
+            while s[right] in str_set:
+                str_set.remove(s[left])
+                left += 1
+            str_set.add(s[right])
+            max_len = max(max_len, right - left + 1)
+        return max_len

reverse-linked-list/prograsshopper.py

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+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        # time complexity: O(n) / memory complexity: O(n)
+        stack = []
+        current = head
+        while current:
+            stack.append(current.val)
+            current = current.next
+
+        dummy_head = ListNode()
+        current = dummy_head
+        while stack:
+            current.next = ListNode(val=stack.pop(), next=None)
+            current = current.next
+        return dummy_head.next