LeetCode 筆記 - 199. Binary Tree Right Side View

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題目在此 199. Binary Tree Right Side View

給定一個 Binary Tree，請計算出從右側看到的 node
image 41

解題思維

這題就是使用 Breadth-First Search 走訪過一次
紀錄每一層最後一個 node 即可

程式碼

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# 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]:
        
        if not root:
            return []
        
        
        upper = [root]
        lower = []
        
        result = []
        while upper:

            result.append(upper[-1].val)
            while upper:
                current_node = upper.pop(0)

                if current_node.left:
                    lower.append(current_node.left)
                if current_node.right:
                    lower.append(current_node.right)
            
            upper = lower
            lower = []
            
        return result

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