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优化 0102.二叉树的层序遍历.md Python3解法
任何在 list 头部进行的操作都会损失一定性能 在 Python 中应该使用 collections.deque 作为队列的数据类型 在该数据类型左右两端追加和弹出元素的时间复杂度都接近O(1)
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@ -87,26 +87,31 @@ public:
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python代码:
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```python
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```python3
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class Solution:
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"""二叉树层序遍历迭代解法"""
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def levelOrder(self, root: TreeNode) -> List[List[int]]:
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results = []
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if not root:
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return []
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return results
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from collections import deque
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que = deque([root])
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while que:
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size = len(que)
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result = []
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for _ in range(size):
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cur = que.popleft()
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result.append(cur.val)
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if cur.left:
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que.append(cur.left)
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if cur.right:
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que.append(cur.right)
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results.append(result)
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queue = [root]
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out_list = []
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while queue:
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length = len(queue)
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in_list = []
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for _ in range(length):
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curnode = queue.pop(0) # (默认移除列表最后一个元素)这里需要移除队列最头上的那个
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in_list.append(curnode.val)
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if curnode.left: queue.append(curnode.left)
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if curnode.right: queue.append(curnode.right)
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out_list.append(in_list)
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return out_list
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return results
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```
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java:
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