deleteMiddle.py

# You are given the head of a linked list. Delete the middle node, and return the head of the modified linked list.

# The middle node of a linked list of size n is the ⌊n / 2⌋th node from the start using 0-based indexing, where ⌊x⌋ denotes the largest integer less than or equal to x.

# For n = 1, 2, 3, 4, and 5, the middle nodes are 0, 1, 1, 2, and 2, respectively.
 

# Example 1:

# [1]
# Input: head = [1,3,4,7,1,2,6]
# Output: [1,3,4,1,2,6]
# Explanation:
# The above figure represents the given linked list. The indices of the nodes are written below.
# Since n = 7, node 3 with value 7 is the middle node, which is marked in red.
# We return the new list after removing this node. 

# 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 deleteMiddle(self, head):
        """
        :type head: Optional[ListNode]
        :rtype: Optional[ListNode]
        """
        if head.next == None:
            return None
        last, current = head, head
        currentDouble = head
        while currentDouble != None and currentDouble.next != None:
            currentDouble = currentDouble.next.next 
            last = current
            current = current.next
        last.next = current.next
        return head