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

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

        fixed_idx = [i for i in range(N+2) if i == p[i]]
        for i in range(len(fixed_idx)-1):
            f, t = fixed_idx[i]+1, fixed_idx[i+1]-1
            if sorted(p[f:t+1]) != list(range(f, t+1)):
                ok = False
                break

            for i in range(f, t+1):
                for j in range(f, t+1):
                    if p[j] == i:
                        i_idx = j
                        break
                if i_idx == i:
                    continue
                for j in range(i_idx, i, -1):
                    assert p[j] == i
                    k = j-1
                    while p[k] == k+1:
                        k -= 1
                    if p[k] == k:
                        for s in range(j-1, k, -1):
                            swap(s)
                            break
                    else:
                        for s in range(k, j):
                            swap(s)

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


if __name__ == '__main__':
    main()