【树-简单】104. 二叉树的最大深度

【题目】

【代码】
【方法1-递归1】

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        self.maxnum=0
        self.depth(root,0)
        return self.maxnum
    
    def depth(self,root,d):
        if not root:
            self.maxnum=max(self.maxnum,d)
            return
        self.depth(root.left,d+1)
        self.depth(root.right,d+1)

【方法2-递归2】

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        else:
            left_depth=self.maxDepth(root.left)+1
            right_depth=self.maxDepth(root.right)+1
            return max(left_depth,right_depth)

【方法3-BFS】借助队列实现

class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        queue=[root]
        depth=0
        while queue:
            size=len(queue)
            for i in range(size):
                node=queue.pop(0)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            depth+=1
        return depth