Find Peak Element.py

# https://leetcode.com/problems/find-peak-element/
# Hak Soo Kim
# 1/25/2022

# 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 oddEvenList(self, head):
        if (head == None):
            return head
        odd, even, evenHead = head, head.next, head.next

        while(even != None and even.next != None):
            odd.next = odd.next.next
            odd = odd.next
            even.next = odd.next
            even = even.next
        odd.next = evenHead
        return head
        """
        :type head: ListNode
        :rtype: ListNode
        """

# Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list.
#
# The first node is considered odd, and the second node is even, and so on.
#
# Note that the relative order inside both the even and odd groups should remain as it was in the input.
#
# You must solve the problem in O(1) extra space complexity and O(n) time complexity.
#
# Example 1:
#
# Input: head = [1, 2, 3, 4, 5]
# Output: [1, 3, 5, 2, 4]
# Example 2:
#
# Input: head = [2, 1, 3, 5, 6, 4, 7]
# Output: [2, 3, 6, 7, 1, 5, 4]
#
# Constraints:
#
# n == number of nodes in the linked list
# 0 <= n <= 104
# -106 <= Node.val <= 106