Given a binary tree, find its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
Note: A leaf is a node with no children.
Example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its depth = 3.
解法
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
#深度优先
def _dfs(self, node, max_level):
#如果当前节点的左右节点都不存在，则直接返回
if not node.left and not node.right:
return max_level
#节点都存在的时候需要继续递归求解
elif node.left and node.right:
return max(self._dfs(node.left,max_level+1),self._dfs(node.right,max_level+1))
#只存在左节点
elif node.left:
return self._dfs(node.left,max_level+1)
#只存在右节点
else:
return self._dfs(node.right,max_level+1)
def maxDepth(self, root: TreeNode) -> int:
#深度优先
if not root:
return 0
max_level = self._dfs(root,1)
return max_level
补上一张图解析
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