populating-next-right-pointers-in-each-node.py

"""
# Definition for a Node.
class Node:
    def __init__(self, val, left, right, next):
        self.val = val
        self.left = left
        self.right = right
        self.next = next
"""
class Solution:
    def connect(self, root):
        if not root: return
        cur, tmp = root, root.left
        while cur.left:
            cur.left.next = cur.right
            if cur.next:
                cur.right.next = cur.next.left
                cur = cur.next
            else:
                cur = tmp
                tmp = cur.left
        return root