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
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