{ "data": { "question": { "questionId": "2196", "questionFrontendId": "2074", "categoryTitle": "Algorithms", "boundTopicId": 1097207, "title": "Reverse Nodes in Even Length Groups", "titleSlug": "reverse-nodes-in-even-length-groups", "content": "
You are given the head
of a linked list.
The nodes in the linked list are sequentially assigned to non-empty groups whose lengths form the sequence of the natural numbers (1, 2, 3, 4, ...
). The length of a group is the number of nodes assigned to it. In other words,
1st
node is assigned to the first group.2nd
and the 3rd
nodes are assigned to the second group.4th
, 5th
, and 6th
nodes are assigned to the third group, and so on.Note that the length of the last group may be less than or equal to 1 + the length of the second to last group
.
Reverse the nodes in each group with an even length, and return the head
of the modified linked list.
\n
Example 1:
\n\n\nInput: head = [5,2,6,3,9,1,7,3,8,4]\nOutput: [5,6,2,3,9,1,4,8,3,7]\nExplanation:\n- The length of the first group is 1, which is odd, hence no reversal occurs.\n- The length of the second group is 2, which is even, hence the nodes are reversed.\n- The length of the third group is 3, which is odd, hence no reversal occurs.\n- The length of the last group is 4, which is even, hence the nodes are reversed.\n\n\n
Example 2:
\n\n\nInput: head = [1,1,0,6]\nOutput: [1,0,1,6]\nExplanation:\n- The length of the first group is 1. No reversal occurs.\n- The length of the second group is 2. The nodes are reversed.\n- The length of the last group is 1. No reversal occurs.\n\n\n
Example 3:
\n\n\nInput: head = [1,1,0,6,5]\nOutput: [1,0,1,5,6]\nExplanation:\n- The length of the first group is 1. No reversal occurs.\n- The length of the second group is 2. The nodes are reversed.\n- The length of the last group is 2. The nodes are reversed.\n\n\n
\n
Constraints:
\n\n[1, 105]
.0 <= Node.val <= 105
给你一个链表的头节点 head
。
链表中的节点 按顺序 划分成若干 非空 组,这些非空组的长度构成一个自然数序列(1, 2, 3, 4, ...
)。一个组的 长度 就是组中分配到的节点数目。换句话说:
1
分配给第一组2
和 3
分配给第二组4
、5
和 6
分配给第三组,以此类推注意,最后一组的长度可能小于或者等于 1 + 倒数第二组的长度
。
反转 每个 偶数 长度组中的节点,并返回修改后链表的头节点 head
。
\n\n
示例 1:
\n\n\n\n\n输入:head = [5,2,6,3,9,1,7,3,8,4]\n输出:[5,6,2,3,9,1,4,8,3,7]\n解释:\n- 第一组长度为 1 ,奇数,没有发生反转。\n- 第二组长度为 2 ,偶数,节点反转。\n- 第三组长度为 3 ,奇数,没有发生反转。\n- 最后一组长度为 4 ,偶数,节点反转。\n\n\n
示例 2:
\n\n\n\n\n输入:head = [1,1,0,6]\n输出:[1,0,1,6]\n解释:\n- 第一组长度为 1 ,没有发生反转。\n- 第二组长度为 2 ,节点反转。\n- 最后一组长度为 1 ,没有发生反转。\n\n\n
示例 3:
\n\n\n\n\n输入:head = [2,1]\n输出:[2,1]\n解释:\n- 第一组长度为 1 ,没有发生反转。\n- 最后一组长度为 1 ,没有发生反转。\n\n\n
\n\n
提示:
\n\n[1, 105]
0 <= Node.val <= 105
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