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67 lines
1.4 KiB
Python
67 lines
1.4 KiB
Python
"""
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102. Binary Tree Level Order Traversal
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Difficulty: Medium
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https://leetcode.com/problems/binary-tree-level-order-traversal/
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──────────────────────────────────────────────────
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Given the root of a binary tree, return the level order traversal of
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its nodes' values. (i.e., from left to right, level by level).
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Example 1:
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Input: root = [3,9,20,null,null,15,7]
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Output: [[3],[9,20],[15,7]]
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Example 2:
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Input: root = [1]
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Output: [[1]]
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Example 3:
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Input: root = []
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Output: []
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Constraints:
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• The number of nodes in the tree is in the range [0, 2000].
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• -1000 <= Node.val <= 1000
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"""
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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from collections import deque
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class Solution:
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# T: O(n) S: O(n)
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def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
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res = []
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q = deque()
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q.append(root)
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while q:
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qLen = len(q)
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level = []
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for i in range(qLen):
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node = q.popleft()
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if node:
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level.append(node.val)
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q.append(node.left)
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q.append(node.right)
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if level:
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res.append(level)
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return res
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