104-maximum-depth-of-binary-tree

代码随想录详细解析

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.

Example 1:

Input: root = [3,9,20,null,null,15,7] Output: 3 Example 2:

Input: root = [1,null,2] Output: 2

My solution：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def maxDepth(self, root):
        """
        :type root: Optional[TreeNode]
        :rtype: int
        """
        if not root:
            return 0
        depth = 0
        queue = deque()
        queue.append(root)
        while queue:
            length = len(queue)
            if length:
                depth += 1
            for i in range(length):
                cur = queue.popleft()
                if cur.left:
                    queue.append(cur.left)
                if cur.right:
                    queue.append(cur.right)
        return depth

recursion solution:

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def maxDepth(self, root):
        """
        :type root: Optional[TreeNode]
        :rtype: int
        """
        return self.getHeight(root)
        
    def getHeight(self,root):
        if not root:
            return 0
        leftHeight = self.getHeight(root.left)
        rightHeight = self.getHeight(root.right)
        return 1 + max(leftHeight,rightHeight)