Today we will do a problem in LeetCode, the original link: finger Offer 32 – print binary tree I from top to bottom

Topic describes

  • Each node of the binary tree is printed from top to bottom, and nodes of the same level are printed from left to right.
  • Such as:
    • Given a binary tree: [3,9,20,null,null,15,7],
    3
   / \
  9  20
    /  \
   15   7
Copy the code
  • Returns:
,9,20,15,7 [3]Copy the code
  • Tip:
The total number of nodes <= 1000Copy the code

Thought analysis

  • Binary tree traversal using dual-ended queues: collections.deque()

code

# Python
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root: return []
        res, queue = [], collections.deque()
        queue.append(root)
        while queue:
            node = queue.popleft()
            res.append(node.val)
            if node.left: queue.append(node.left)
            if node.right: queue.append(node.right)
        return res
Copy the code

conclusion

  • collections.deque()
    • Append () : append function
    • Popleft () : fetch data from the header

The appendix

  • Leetcode-cn.com/problems/co…

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