feat: reverse-linked-list, valid-parentheses 풀이

Author: gusdn0828

reverse-linked-list/saysimple.py

@@ -0,0 +1,27 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+# TC, SC: O(n), O(1)
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if not head:
+            return None
+
+        if not head.next:
+            return head
+
+        prev_node = head
+        node = prev_node.next
+        prev_node.next = None
+
+        while node.next:
+            next_node = node.next
+            node.next = prev_node
+            prev_node = node
+            node = next_node
+
+        node.next = prev_node
+
+        return node

valid-parentheses/saysimple.py

@@ -0,0 +1,23 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        arr = []
+
+        for c in s:
+            if c in ["(", "[", "{"]:
+                arr.append(c)
+                continue
+            else:
+                if not arr:
+                    return False
+                b = arr.pop()
+                if b == "(" and c == ")":
+                    continue
+                if b == "[" and c == "]":
+                    continue
+                if b == "{" and c == "}":
+                    continue
+                return False
+        if arr:
+            return False
+        else:
+            return True