16天【代码随想录算法训练营34期】第六章 二叉树part03（● 104.二叉树的最大深度 559.n叉树的最大深度 ● 111.二叉树的最小深度 ● 222.完全二叉树的节点个数）

104.二叉树的最大深度

# 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: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        else:
            left = self.maxDepth(root.left)
            right = self.maxDepth(root.right)
            return 1 + max(left, right)

111.二叉树的最小深度

# 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 minDepth(self, root: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        else:
            left = self.minDepth(root.left)
            right = self.minDepth(root.right)
            if root.left and root.right:
                return 1+min(left, right)
            elif root.left is None and root.right:
                return 1+right
            elif root.right is None and root.left:
                return 1+left
            else:
                return 1

222.完全二叉树的节点个数

# 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 countNodes(self, root: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        else:
            left = self.countNodes(root.left)
            right = self.countNodes(root.right)
            return 1+left+right