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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        TreeNode rt = root;
        List<Integer> lt = new ArrayList<Integer>();
        inorderTraversal1(rt, lt);
        return lt;
    }
    
    public void inorderTraversal1(TreeNode rt, List<Integer> lt) {
        if(rt == null) 
            return;
        inorderTraversal1(rt.left, lt);
        lt.add(rt.val);
        inorderTraversal1(rt.right, lt);
    }
}