JAVA算法练习题day29

37.二叉树的最大深度

# 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"""#层序遍历的遍历次数#dfs我不知道怎么做#递归：问题（整个树的高度）拆成子问题（子树的高度）：最大深度等于{max(左子树高度,右子树高度)+1}#这个+1就是把自己这个节点给算上if root is None:return 0else:left_height = self.maxDepth(root.left)right_height = self.maxDepth(root.right)return max(left_height,right_height)+1

# 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 root is None:return 0#初始化队列queue = deque([root])depth = 0while queue:level_size = len(queue)for _ in range(level_size):node = queue.popleft()if node.left is not None:queue.append(node.left)if node.right is not None:queue.append(node.right)depth+=1return depth