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  • leetcode 206. Reverse Linked List

    Reverse a singly linked list.

    click to show more hints.

    # Definition for singly-linked list.
    # class ListNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.next = None
    
    class Solution(object):
        def reverseList(self, head):
            """
            :type head: ListNode
            :rtype: ListNode
            """
            if not head: return None
            pre_node = head
            next_node = head.next
            pre_node.next = None
            while next_node:
                tmp = next_node.next
                next_node.next = pre_node
                pre_node = next_node
                next_node = tmp
            return pre_node        

    精简下代码:

    # Definition for singly-linked list.
    # class ListNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.next = None
    
    class Solution(object):
        def reverseList(self, head):
            """
            :type head: ListNode
            :rtype: ListNode
            """
            if not head: return None
            pre_node = None
            cur_node = head
            while cur_node:
                tmp = cur_node.next
                cur_node.next = pre_node
                pre_node = cur_node
                cur_node = tmp
            return pre_node        

    递归解:

    # Definition for singly-linked list.
    # class ListNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.next = None
    
    class Solution(object):
        def reverseList(self, head):
            """
            :type head: ListNode
            :rtype: ListNode
            """
            def reverse_node(pre_node, cur_node):
                if not cur_node: return pre_node
                next_node = cur_node.next
                cur_node.next = pre_node
                return reverse_node(cur_node, next_node)
                 
            if not head: return None
            new_head = reverse_node(head, head.next)
            head.next = None
            return new_head                                  

    dfs

    # Definition for singly-linked list.
    # class ListNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.next = None
    
    class Solution(object):
        def reverseList(self, head):
            """
            :type head: ListNode
            :rtype: ListNode
            """
            if not head or not head.next: return head
            node = self.reverseList(head.next)
            head.next.next = head
            head.next = None
            return node                

    记得程序员面试金典里专门提过!

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  • 原文地址:https://www.cnblogs.com/bonelee/p/8687153.html
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