606. 根据二叉树创建字符串

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public String tree2str(TreeNode t) {
        if (t==null)
            return "";
        if (t.left==null && t.right==null)
            return t.val+"";
        else if (t.left==null)
            return t.val+"()"+"("+tree2str(t.right)+")";
        else if(t.right==null)
            return t.val+"("+tree2str(t.left)+")";
        return  t.val+"("+tree2str(t.left)+")"+"("+tree2str(t.right)+")";
    }
}