C. Twin Polynomialstime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputA polynomial $$$f(x) = a_0 + a_1x + a_2x^2 + \ldots + a_nx^n$$$ is called a valid polynomial of degree $$$n$$$ if and only if $$$a_i$$$ is a non-negative integer for all $$$0 \le i \le n$$$ and $$$a_n$$$ is not $$$0$$$.For a valid polynomial $$$f(x) = a_0 + a_1x + a_2x^2 + \ldots + a_nx^n$$$ of degree $$$n$$$, its twin polynomial $$$g(x)$$$ is defined as: $$$$$$ g(x) = \sum_{i=0}^n i \cdot x^{a_i} $$$$$$ For example, for $$$f(x) = 1 + 2x + 2x^3$$$, its twin polynomial is:$$$$$$ g(x) = 0 \cdot x^{1} + 1 \cdot x^{2} + 2 \cdot x^{0} + 3 \cdot x^{2} = 0+x^2+2+3x^2= 2 + 4x^2 $$$$$$A valid polynomial $$$f(x)$$$ of degree $$$n$$$ is called cool if and only if $$$f(x) = g(x)$$$. In other words, a valid polynomial of degree $$$n$$$ is cool if and only if its twin polynomial equals itself.You are given an incomplete valid polynomial $$$f(x) = a_0 + a_1x + a_2x^2 + \ldots + a_nx^n$$$ of degree $$$n$$$. Some of $$$a_i$$$ have been determined, while others have not been determined. Additionally, it is guaranteed that $$$a_0$$$ and $$$a_n$$$ are not determined.Please count the number of cool valid polynomials of degree $$$n$$$ that can be found by determining all undetermined $$$a_i$$$'s. Since the answer may be large, you need to output it modulo $$$1\,000\,000\,007$$$.InputEach test contains multiple test cases. The first line contains the number of test cases $$$t$$$ ($$$1 \le t \le 10^4$$$). The description of the test cases follows. For each test case, the first line contains an integer $$$n$$$ ($$$1 \leq n \leq 4 \cdot 10^5$$$).The second line contains $$$n+1$$$ integers $$$a_0, a_1, \ldots, a_n$$$ ($$$-1 \leq a_i \leq 10^9$$$). Here, $$$a_i=-1$$$ means $$$a_i$$$ has not been determined, while $$$a_i \neq -1$$$ means $$$a_i$$$ has been determined as its value.It is guaranteed that $$$a_0$$$ and $$$a_n$$$ are always $$$-1$$$ in the input.It is guaranteed that the sum of $$$n$$$ over all test cases does not exceed $$$4 \cdot 10^5$$$.OutputFor each test case, output the number of cool valid polynomials of degree $$$n$$$ found by determining the undetermined $$$a_i$$$'s, modulo $$$1\,000\,000\,007$$$.ExampleInput61-1 -12-1 2 -12-1 -1 -13-1 -1 3 -13-1 2 3 -15-1 -1 -1 1 0 -1Output113203NoteIn the first test case, only $$$f(x) = x$$$ satisfies the condition above.In the second test case, only $$$f(x) = x^2 + 2x$$$ satisfies the condition above.In the third test case, $$$f(x) = 2x^2 + x$$$, $$$f(x) = x^2 + 2x$$$, and $$$f(x) = 2x^2 + 1$$$ satisfy the condition above.