0. 题目

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.

1. c++版本

方法1递归方式，其实左子树或者右子树的最大深度+当前root

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (!root)
            return 0;
        return max(maxDepth(root->left), maxDepth(root->right)) + 1;
    }
};

版本2，利用层序遍历, 求二叉树的深度！

  int maxDepth(TreeNode* root) {
        queue<TreeNode *> fatherQueue, childQueue;
        int depth=0;
        if (root) {
            fatherQueue.push(root);
            depth++;
        }
        while (!fatherQueue.empty()) {
            root = fatherQueue.front();
            fatherQueue.pop();
            if (root->left)
                childQueue.push(root->left);
            if (root->right)
                childQueue.push(root->right);
            if (fatherQueue.empty() && !childQueue.empty()) {
                swap(fatherQueue, childQueue);
                depth++;
            }
        }
        return depth;
    }

2. python版本

如何c++版本，采用递归方式

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0
        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1