Package g2001_2100.s2074_reverse_nodes_in_even_length_groups

Class Solution

  • public class Solution
extends Object
    2074 - Reverse Nodes in Even Length Groups.

    Medium

    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,

    • The 1st node is assigned to the first group.
    • The 2nd and the 3rd nodes are assigned to the second group.
    • The 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.

    Example 1:

    Input: head = [5,2,6,3,9,1,7,3,8,4]

    Output: [5,6,2,3,9,1,4,8,3,7]

    Explanation:

    • The length of the first group is 1, which is odd, hence no reversal occurs.

    • The length of the second group is 2, which is even, hence the nodes are reversed.

    • The length of the third group is 3, which is odd, hence no reversal occurs.

    • The length of the last group is 4, which is even, hence the nodes are reversed.

    Example 2:

    Input: head = [1,1,0,6]

    Output: [1,0,1,6]

    Explanation:

    • The length of the first group is 1. No reversal occurs.

    • The length of the second group is 2. The nodes are reversed.

    • The length of the last group is 1. No reversal occurs.

    Example 3:

    Input: head = [1,1,0,6,5]

    Output: [1,0,1,5,6]

    Explanation:

    • The length of the first group is 1. No reversal occurs.

    • The length of the second group is 2. The nodes are reversed.

    • The length of the last group is 2. The nodes are reversed.

    Constraints:

    • The number of nodes in the list is in the range [1, 105].
    • 0 <= Node.val <= 105

    • Constructor Detail

      • Solution

        public Solution()

    • Method Detail

      • reverseEvenLengthGroups

        public ListNode reverseEvenLengthGroups​(ListNode head)