public void BuildTreeLikeA_Ok()
    {
        var root = TreeUtil.BuildTreeLikeA(2);

        Assert.NotNull(root);
        Assert.Equal(1, root.Val);
    }
    public void GetPathSumFromBottomByStack_Ok(int n)
    {
        var root = TreeUtil.BuildTreeLikeA(n);

        Assert.NotNull(root);
        Assert.Equal(1, root.Val);

        var sums       = TreePathSum.GetPathSumFromBottomByStack(root);
        var onePathSum = 2 * n + 1;

        Assert.Equal(4, sums.Count);
        Assert.Equal(onePathSum, sums[0]);
    }