73 lines
1.6 KiB
Markdown
73 lines
1.6 KiB
Markdown
# Find Maximum depth of binary tree
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[LeetCode problem](https://leetcode.com/problems/maximum-depth-of-binary-tree/)
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Given the root of a binary tree, return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
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Example: input: [3,9,20,null,null,15,7], output: 3.
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## LeetCode initial code
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```python
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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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class Solution:
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def maxDepth(self, root: Optional[TreeNode]) -> int:
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```
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## Recursive approach
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Depth first
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```python
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def maxDepth(self, root: Optional[TreeNode]) -> int:
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def max_depth(root, depth):
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if not root: return depth
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return max(max_depth(root.left, depth+1), max_depth(root.right, depth+1))
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return max_depth(root, 0)
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```
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## Iterative solution
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Breadth first
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```python
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def maxDepth(self, root: Optional[TreeNode]) -> int:
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if not root:
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return 0
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queue = [root]
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depth = 0
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while True:
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if not queue:
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break
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node_count = len(queue)
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depth += 1
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while node_count > 0:
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node = queue[0]
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queue.pop(0)
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if node.left:
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queue.append(node.left)
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if node.right:
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queue.append(node.right)
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node_count -= 1
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return depth
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```
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