199. Binary Tree Right Side View

Question: Binary Tree Right Side View

Solution

1. 先找出每一層有誰 → 分層 → BFS → queue
2. 再找該層最右邊是誰
1. 該層每一個 node ，從最前面開始取出: queue.popleft()
2. 取出後，看他的 left & right children，放入 queue 的後面: queue.append(left/right children)
3. 取到該層的最後一個值，記起來: ans.append(last_node.val)

# Definition for a binary tree node.

# class TreeNode:

# def __init__(self, val=0, left=None, right=None):

# self.val = val

# self.left = left

# self.right = right

class Solution:

def rightSideView(self, root: Optional[TreeNode]) -> List[int]:

ans = list()

if root == None:

return ans

q = deque([root])

while q:

for i in range(len(q)):

node = q.popleft()

if node.left:

q.append(node.left)

if node.right:

q.append(node.right)

ans.append(node.val)

return ans

Video Solution