def main():
    T = int(input())
    for i in range(T):
        N = int(input())
        p = [0] + list(map(int, input().split())) + [N+1]
        fixed_idx = [i for i in range(N+2) if i == p[i]]

        ok = True
        ans = []

        def swap(i):
            assert i != p[i]
            assert i+1 != p[i+1]
            ans.append(i)
            p[i], p[i+1] = p[i+1], p[i]

        for i in range(len(fixed_idx)-1):
            f, t = fixed_idx[i], fixed_idx[i+1]
            if sorted(p[f+1:t]) != list(range(f+1, t)):
                ok = False
                break

            for i in range(f+1, t):
                for j in range(i, t):
                    if p[j] == i:
                        i_idx = j
                if i_idx == i:
                    continue

                for j in range(i_idx, i, -1):
                    if p[j-1] == j and j != i+1:
                        swap(j-2)
                    swap(j-1)

        if not ok:
            print(-1)
        else:
            assert p == sorted(p)
            print(len(ans))
            print(*ans)


if __name__ == '__main__':
    main()