重建二叉树

    //解题思路：
    //1、用前序确定root节点
    //2、然后在中序中用root节点左右分割，就分辨是左右子树了。
    //3、在左右子树中，用递归重复1、2
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if(pre == null || pre.length == 0 || in ==null || in.length == 0) {
            return null;
        }
        TreeNode root = new TreeNode(pre[0]);
        for(int i = 0; i<in.length; i++) {
            if(pre[0] == in[i]) {
                root.left = reConstructBinaryTree(Arrays.copyOfRange(pre, 1, i+1), Arrays.copyOfRange(in, 0, i));
                root.right = reConstructBinaryTree(Arrays.copyOfRange(pre, i+1 , pre.length), Arrays.copyOfRange(in, i+1, in.length));
            }
        }
        return root;
    }