Binary Tree Inorder Traversal @leetcode

InorderTraversal.java

package leetcode.tree;

import java.util.ArrayList;
import java.util.Stack;

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

public class InorderTraversal {
	
	public ArrayList<Integer> inorderTraversal(TreeNode root) {
		TreeNode node = root;
		
		Stack<TreeNode> stack = new Stack<TreeNode>();
		ArrayList<Integer> arrayList = new ArrayList<Integer>(); 
		
		while (node != null || stack.size() > 0) {
			while (node != null) {
				stack.push(node);
				node = node.left;
			}
			
			if (stack.size() > 0) {
				node = stack.pop();
				arrayList.add(node.val);
				node = node.right;
			}
		}
		
		return arrayList;
    }
	
	// TreeNode 
	public class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;
		TreeNode (int x) {
			val = x;
		}
	}
	
}