public void BuildTreeTest()
        {
            var solution = new _105_ConstructBinaryTreeFromPreorderAndInorderTraversal();
            var result   = solution.BuildTree(new int[] { 3, 9, 20, 15, 7 }, new int[] { 9, 3, 15, 20, 7 });

            AssertHelper.AssertTree(new int?[] { 3, 9, 20, null, null, 15, 7 }, result);
        }
        public void BuildTreeTest_Empty()
        {
            var solution = new _105_ConstructBinaryTreeFromPreorderAndInorderTraversal();
            var result   = solution.BuildTree(new int[] {}, new int[] {});

            Assert.IsNull(result);
        }