Add Java solution for 94. Binary Tree Inorder Traversal

Author: gnohgnij

java/0094-binary-tree-inorder-traversal.java

@@ -0,0 +1,37 @@
+class Solution {
+    public List<Integer> inorderTraversal(TreeNode root) {
+        //iterative
+        List<Integer> res = new ArrayList<>();
+        if(root == null) return res;
+
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode node = root;
+        while(!stack.isEmpty() || node != null) {
+            if(node != null) {
+                stack.push(node);
+                node = node.left;
+            } else {
+                node = stack.pop();
+                res.add(node.val);
+                node = node.right;
+            }
+        }
+
+        return res;
+
+        //recursive
+        // List<Integer> res = new ArrayList<>();
+        // dfs(root, res);
+        // return res;
+    }
+
+    // public void dfs(TreeNode n, List<Integer> res) {
+    //     if(n == null) {
+    //         return;
+    //     }
+        
+    //     dfs(n.left, res);
+    //     res.add(n.val);
+    //     dfs(n.right, res);
+    // }
+}