[Python] LeetCode - Reverse Linked List

Problem

 

Solving Process

head를 돌면서 새로운 노드를 만든다

그리고 새로운 노드의 val을 head.val로 설정하고

next의 값은 전에 만들었던 노드로 연결한다.

 

+

정석의 방법은 next의 방향을 뒷 노드로 바꾸는 것 !!

 

Solution

# 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]:
        curr = answer = ListNode()
        while head:
            node = ListNode(val=head.val, next=curr.next)
            curr.next = node
            head = head.next
        return answer.next

 

내가 푼 방법!

 

정석 방법도 기록해두겠다. (next의 방향을 역순으로 바꾸기)

class Solution(object):
    def reverseList(self, head):
        # Initialize prev pointer as NULL...
        prev = None
        # Initialize the curr pointer as the head...
        curr = head
        # Run a loop till curr points to NULL...
        while curr:
            # Initialize next pointer as the next pointer of curr...
            next = curr.next
            # Now assign the prev pointer to curr’s next pointer.
            curr.next = prev
            # Assign curr to prev, next to curr...
            prev = curr
            curr = next
        return prev       # Return the prev pointer to get the reverse linked list...