Number of ways to get from $(0, 0)$ to $(x, y)$ with moves $(x+ 1, y + 1)$, $(x - 1, y + 1)$ and additional constraint. How many ways are there to get from $(0, 0)$ to $(x, y)$ in coordinates system assuming that from $(i, j)$ you can move to $(i + 1, j + 1)$, $(i - 1, j + 1)$ and if you make some moves of the second type in a row then you have to do at least the same amount of moves of the first type in a row. For example, there are $5$ ways to get from $(0, 0)$ to $(-1, 5)$ and $0$ ways to get to $(-2, 5)$. You can assume that $(x, y)$ lies in a second quadrant.
What I've found out is that the problem is equivalent to calculating how many binary sequences of length $y$ are there such that there are $x$ more ones, than zeros and after each contiguous sequence of zeros there must be contiguous sequence of ones of length at least the same. For example, a correct sequence is $1111001110101000111000011111$.
 A: Suppose we know how to answer the arguably easier question

(Problem 2) How many ways are there to get from the origin (0,0) to (x,y) (where $(x,y) \in \mathbb{Z}^2$) only using the moves +(1,0), +(0,1)?

Now define the change of variables $\mathbb{Z}^2 \to \mathbb{Z}^2$ given by the matrix $T = \begin{pmatrix} 1 & -1 \\ 1 & 1 \end{pmatrix} $.
$T$ has the property that it maps the moves $+(1,0)$ to $+(1,1)$ and $+(0,1)$ to $+(-1,1)$. You can verify:

The number of ways to get from (0,0) to (x,y) using moves +(1,0) and +(0,1) is the same as the number of ways to get from T(0,0) = (0,0) to T(x,y) = (x-y, x+y) using the moves +(1,1), +(-1,1).

Few things to note:


*

*T is not surjective, so you cannot reach every point (x,y) using +(1,1), +(-1,1), for instance (x,y) = (0,1).

*T has a "left-inverse" $T^{-1} = \frac{1}{2}\begin{pmatrix} 1 & 1 \\ -1 & 1 \end{pmatrix}$, i.e. $T^{-1}T(x,y) = (x,y)$, which should help you translate between the two problems. Also you can use this to derive a condition under which (x,y) is reacheable.

*Problem 2 can be interpreted as counting the number of ways to arrange $x$ zeroes and $y$ ones in a binary number of length $x+y$. Also: $x+y$ is the value of the $y$-coordinate after applying $T$ to $(x,y)$, which matches with your observation.
