116.py

from collections import deque


# Name: Populating Next Right Pointers in Each Node
# Link: https://leetcode.com/problems/populating-next-right-pointers-in-each-node/
# Method: Modified BFS
# Time: O(n)
# Space: O(log(depth))
# Difficulty: Medium


# 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: "Node") -> "Node":
 if not root:
 return None

 level_now = deque([root])
 next_level = deque()
 while level_now:
 node_now = level_now.popleft()
 if node_now.left:
 next_level.append(node_now.left)
 next_level.append(node_now.right)
 node_now.next = level_now[0] if level_now else None

 if not level_now:
 level_now = next_level
 next_level = deque()

 return root

 def brige_builder_rec(node: "Node") -> "Node":

 if not node.left: # We're at a leaf
 return None

 left_side = node.left
 right_side = node.right

 while left_side and right_side:
 left_side.next = right_side
 left_side = left_side.right
 right_side = right_side.left

 brige_builder_rec(node.left)
 brige_builder_rec(node.right)

 def brige_builder_next(root: "Node") -> "Node":
 if not root:
 return None

 node_now = root
 next_node = root.left

 while node_now.left:
 node_now.left.next = cur.right

 if node_now.next: # Can do rightwards
 node_now.right.next = node_now.next.left
 node_now = node_now.next
 else:
 node_now = next_node
 next_node = node_now.left