reverse-linked-list solution (py)

Author: hi-rachel

reverse-linked-list/hi-rachel.py

@@ -0,0 +1,44 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+
+"""
+1. Stack 활용 (LIFO)
+- LinkedList의 모든 원소를 Stack에 넣고 꺼냄
+TC: O(n) time
+SC: O(n) space
+
+2. 최적화 풀이
+- 현재 LinkedList를 거꾸로 뒤짚기
+TC: O(n) -> LinkedList를 딱 한 번 순회
+SC: O(1) -> 변수를 포인터 2개만 사용
+"""
+
+# Stack 풀이
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        stack = []
+        node = head
+        while node:
+            stack.append(node)
+            node= node.next
+
+        dummy = ListNode(-1)
+        node = dummy
+        while stack:
+            node.next = stack.pop()
+            node = node.next
+        node.next = None
+        return dummy.next
+    
+# 최적화
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev, curr = None, head
+        while curr:
+            temp_next = curr.next
+            curr.next = prev
+            prev, curr = curr, temp_next
+        return prev