22911번 - Hidden Pancakes 서브태스크다국어

We are cooking N pancakes in total. We cook one pancake with a 1 centimeter (cm) radius, one with a 2 cm radius, one with a 3 cm radius, ..., and one with an N cm radius, not necessarily in that order. After we cook the first pancake, we just lay it on a plate. After we cook each subsequent pancake, we lay it on top of the previously made pancake, with their centers coinciding. In this way, a pancake is visible from the top of the stack when we first add it. A pancake only becomes hidden if we later cook another pancake with a larger radius.

For example, say we cook 4 pancakes. We first cook the pancake with radius 3 cm, and it is visible. Then, we cook the pancake with radius 1 cm, lay it on top of the first one and both are visible. Third, we cook the pancake with radius 2 cm, and now that covers the previous pancake, but not the first one, so 2 pancakes remain visible in total. Finally, we cook the pancake with radius 4 cm which covers the other pancakes leaving only 1 visible pancake. The picture below illustrates the state of the stack after each pancake is cooked. Within each stack, the fully colored pancakes are visible and the semi-transparent pancakes are not visible.

Let V_i be the number of visible pancakes when the stack contains exactly i pancakes. In the example above, V₁ = 1, V₂ = 2, V₃ = 2, and V₄ = 1.

Given the list V₁, V₂, …, V_N, how many of the N! possible cooking orders yield those values? Since the output can be a really big number, we only ask you to output the remainder of dividing the result by the prime 10⁹+7 (1000000007).

The first line of the input gives the number of test cases, T. T test cases follow, each described with two lines. The first line of a test case contains a single integer N, the number of pancakes we cook. The second line of a test case contains N integers V₁, V₂, ..., V_N, representing the number of visible pancakes after we cook 1, 2, ..., N pancakes, respectively.

For each test case, output one line containing Case #x: y, where x is the test case number (starting from 1) and y is the number of cooking orders of N pancakes that yield the given numbers of visible pancakes after each step, modulo the prime 10⁹+7 (1000000007).

• 1 ≤ T ≤ 100.
• 1 ≤ V_i ≤ i, for all i.

시간 제한: 30 초

• 2 ≤ N ≤ 13.

시간 제한: 40 초

• 2 ≤ N ≤ 10⁵.