[LeetCode] Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

   1
    \
     2
    /
   3
return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

[Solution].java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<Integer> inorderTraversal(TreeNode root) {
        ArrayList<Integer> result = new ArrayList<Integer>();
        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode run = root;
        while(run != null){
            stack.add(run);
            run = run.left;
        }
        while(!stack.isEmpty()){
            run = stack.pop();
            result.add(run.val);
            run = run.right;
            while(run != null){
                stack.add(run);
                run = run.left;
            }
        }
        return result;
    }
}