9/100. Reverse Linked List

• 非递归算法：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        pFront = None
        pNode = head
        while pNode:
            pNext = pNode.next
            pNode.next = pFront
            pFront = pNode
            pNode = pNext
        return pFront

• 递归算法：

    def reverseList(self, head):
        if not head or not head.next:
            return head
        pre = self.reverseList(head.next)
        head.next.next = head
        head.next = None
        return pre