206.反转链表

206.反转链表

解题思路

JavaScript解法代码

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {
    // 只有头节点或头节点为空（边界条件）
    if(!head || !head.next) return head;

    let current = head,pre=null,temp=null;
    while(current){
        temp = current.next
        current.next = pre
        pre = current
        current = temp
    }
    return pre
    
};

Python解法代码

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """。
        current = head
        temp = None
        pre = None
        while(current):
            temp = current.next
            current.next = pre
            pre = current
            current = temp  
        return pre
        

写了递归，二刷时回来补充。