For example:

Given binary tree {1,#,2,3},

1    \     2    /   3

 

return [1,3,2].

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {        List
     
       re_list = new ArrayList
      
       ();    //中序遍历二叉树    public void IFS(TreeNode N) {        if(N!=null) {            if(N.left!=null) IFS(N.left);            re_list.add(N.val);            if(N.right!=null) IFS(N.right);        }    }         public List
       
         inorderTraversal(TreeNode root) {        IFS(root);        return re_list;    }}