Difficulty: HARD

Given the head of a singly linked list represented as a ListNode, and two zero-indexed positions x and y, write a function swap_node which swaps the positions of nodes x and y and returns the new head. Note that you cannot simply swap the values of these nodes, as these nodes do not have values. Instead, you must swap these two using pointer manipulation (i.e., modifying the next references of the involved nodes inside the list).

A ListNode is defined as:

class ListNode:
	**next = None**

Example:

Input:

linked_list = ListNode(0x01) -> ListNode(0x02) -> ListNode(0x03) 
# Here, imagine that '0x0_' refer to their memory locations.
head = 0x01
x = 1
y = 2

Output:

def swap_node(head, x, y) ->  ListNode(0x01)  -> ListNode(0x03) -> ListNode(0x02)