143. 重排链表

原题

https://leetcode.cn/problems/reorder-list/description/

思路

列表+虚拟节点

复杂度

时间：O(n)
空间：O(n)

Python代码

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reorderList(self, head: Optional[ListNode]) -> None:
        """
        Do not return anything, modify head in-place instead.
        """
        arr = []
        while head:
            arr.append(head)
            head = head.next 
        l, r = 0, len(arr) - 1 
        dummy = p = ListNode(-1, head)
        i = 0
        while l <= r:
            if i % 2 == 0:
                p.next = arr[l]
                l += 1
            else:
                p.next = arr[r]
                r -= 1 
            p = p.next 
            i += 1 
        p.next = None
       

Go代码

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func reorderList(head *ListNode) {
	// 切片储存节点
	arr := []*ListNode{}
	for head != nil {
		arr = append(arr, head)
		head = head.Next
	}
	l, r := 0, len(arr)-1
	dummy := &ListNode{Val: -1, Next: head}
	p := dummy
	i := 0
	for l <= r {
		if i%2 == 0 {
			p.Next = arr[l]
			l++
		} else {
			p.Next = arr[r]
			r--
		}
		p = p.Next
		i++
	}
	p.Next = nil
}