reverse-linked-list solution

Author: devyejin

reverse-linked-list/devyejin.py

@@ -0,0 +1,42 @@
+# Definition for singly-linked list.
+from typing import Optional
+
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+# time complexity O(n), space complexity O(1)
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev = None # 뒤집힌 리스트의 시작 노드
+        curr = head # 현재 탐색 중인 노드
+
+        while curr:
+            temp = curr.next # 다음 노드 기억
+            curr.next = prev
+            # 다음 포인터로 이동하기 전 현재노드를 이전 노드로 변경
+            prev = curr
+            # 포인터 이동
+            curr = temp
+
+        return prev
+
+# time complexity O(n), space complexity O(n)
+# class Solution:
+    # def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+    #     stack = []
+    #     while head:
+    #         stack.append(head)
+    #         head = head.next
+    #
+    #     dummy = ListNode()
+    #     curr = dummy
+    #     while stack:
+    #         node = stack.pop()
+    #         node.next = None
+    #         curr.next = node
+    #         curr = curr.next
+    #
+    #     return dummy.next