9703번 - Anti-Arithmetic Permutation 다국어

We call a permutation p₀, p₁, ... , p_n-1 of integers 0, 1, ... , n-1 anti-arithmetic, when there are no three-term arithmetic series in this permutation, i.e. there are no such three indices i < j < k, that integers p_i, p_j, p_k make an arithmetic series. For example, the series of integers 3, 1, 0, 4, 2 is an anti-arithmetic permutation of integers 0, 1, 2, 3, 4. The series 0, 5, 4, 3, 1, 2 is not an antiarithmetic permutation, because its first, fifth and sixth term: 0, 1, 2 form an arithmetic series (as well as its second, fourth and fifth term: 5, 3, 1 and second third and fourth term: 5, 4, 3 form arithmetic series). Given a permutation of length n determine whether the given permutation is anti-arithmetic or not.

Input starts with an integer T, the number of test cases.

Each test case consists of two lines. First line contains an integer n. Next line contains n integers separated by a single space. These n integers denotes a permutation of 0, 1, .., n-1. n is between 3 and 50 inclusive.

For each test case, the output contains a line in the format Case #x: M, where x is the case number (starting from 1) and M is “YES” when the given permutation is anti-arithmetic or “NO” otherwise. Quotes are for clarity only.