116. Populating Next Right Pointers in Each Node

116. Populating Next Right Pointers in Each Node

這一題要考的點是對進行 BFS 時，是否可以按照樹的層級來遍歷。

"""
# 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]':
        
        if not root:
            return root
        
        queue = deque([root])
        
        while queue:
            size = len(queue)
            while size > 0:
                node = queue.popleft()
                if size == 1:
                    node.next = None
                else:
                    node.next = queue[0]
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
                size -= 1
        
        return root
                

"""
# 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 root

        queue = deque([root])

        while queue:
            size = len(queue)
            for i in range(size):
                node = queue.popleft()
                if i < size - 1:
                    node.next = queue[0]
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
        return root