feat: add 104

Author: Blankj

note/104/README.md

@@ -0,0 +1,42 @@
+# [Maximum Depth of Binary Tree][title]
+
+## Description
+
+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.
+
+**Tags:** Tree, Depth-first Search
+
+
+## 思路
+
+题意是找到二叉树的最大深度，很明显，深搜即可，每深入一次节点加一即可，然后取左右子树的最大深度。
+
+``` java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+ class Solution {
+     public int maxDepth(TreeNode root) {
+         if (root == null) return 0;
+         return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
+     }
+ }
+```
+
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我GitHub上的LeetCode题解：[awesome-java-leetcode][ajl]
+
+
+
+[title]: https://leetcode.com/problems/maximum-depth-of-binary-tree
+[ajl]: https://github.com/Blankj/awesome-java-leetcode