Populating_Next_Right_Pointers_in_Each_Node.py

"""
# Definition for a Node.
class Node:
    def __init__(self, val: int = 0, left: 'Node' = None, right: 'Node' = None, next: 'Node' = None):
        self.val = val
        self.left = left
        self.right = right
        self.next = next
"""

class Solution:
    def connect(self, root: 'Optional[Node]') -> 'Optional[Node]':
        cur,nxt=root,root.left if root else None
        while cur and nxt:
            cur.left.next=cur.right
            if cur.next:
                cur.right.next=cur.next.left
            cur=cur.next
            if not cur:
                cur=nxt
                nxt=cur.left
        return root