Binary Tree Inorder Traversal Problem

Problem Description
Easy level

Given a binary tree, return the inorder traversal of its nodes’ values. Binary Tree Inorder Traversal is to parse left child node, then root, then right child node

Example
Given binary tree {1,#,2,3},

return [1,3,2].

Solution:


    /**
     * @param root: The root of binary tree.
     * @return: inorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
    	ArrayList<Integer> lst = new ArrayList<Integer>();
    	
    	traver(lst, root);
    	
		return lst;
    }
	
	void traver(ArrayList<Integer> lst, TreeNode node) {
		if(node == null)  return;
		
		if(node.left != null) traver(lst, node.left);
		lst.add(node.val);
		if(node.right != null)  traver(lst, node.right);
	}