LeetCode | 算法：求二叉树是否相同&树的最大深

100. Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def isSameTree(self, p, q):
        """
        :type p: TreeNode
        :type q: TreeNode
        :rtype: bool
        """
        # 递归出口
        if not p and not q:     #p,q为空
            return True
        
        elif not p or not q:    #p,q有一个为空，一个不为空
            return False
        
        elif p.val!=q.val:      #p,q均不空，但是值不相等
            return False         
        
        else:
            return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)
        

104. 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.

算法思想：采用宽度优先搜索，一层层处理，在处理当前层时，最大深度+1，将队列中所有元素出队，并将这些元素的孩子节点全部入队，以此循环，直到队列为空。

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        
        max_depth = 0
        que = collections.deque()
        que.append(root)
        
        while que:
            max_depth += 1
            num_children = len(que)
            for _ in range(num_children):
                node = que.popleft()
                if node.left:
                    que.append(node.left)
                if node.right:
                    que.append(node.right)
        
        return max_depth