def main():
    T = int(input())
    for i in range(T):
        N = int(input())
        p = [0] + list(map(int, input().split())) + [N+1]

        m = [0 for i in range(N+2)]
        for i in range(1, N+2):
            m[i] = max(m[i-1], p[i])

        ans = []

        def swap(i):
            if i == p[i] or i+1 == p[i+1]:
                return False
            if i+1 == p[i] and max(m[i-1], p[i+1]) != i:
                return False
            if i == p[i+1] and m[i-1] != i-1:
                return False

            ans.append(i)
            p[i], p[i+1] = p[i+1], p[i]
            m[i] = max(m[i-1], p[i])
            m[i+1] = max(m[i], p[i+1])
            return True

        while True:
            for i in range(1, N):
                if p[i] > p[i+1] and swap(i):
                    break
            else:
                break

        if p == sorted(p):
            print(len(ans))
            print(*ans)
        else:
            print(-1)


if __name__ == '__main__':
    main()