feat: 104. Maximum Depth of Binary Tree solution

(cherry picked from commit c08337da842878a78cbf56d19d4f4618d8e6bb2e)

Author: Yiseull

maximum-depth-of-binary-tree/Yiseull.java

@@ -0,0 +1,29 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+
+    public int maxDepth(TreeNode root) {
+        return dfs(root);
+    }
+
+    private int dfs(TreeNode node) {
+        if (node == null) {
+            return 0;
+        }
+
+        return 1 + Math.max(dfs(node.left), dfs(node.right));
+    }
+}