import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)


def main():
    N = int(input())
    P = list(map(lambda x: int(x) - 1, input().split()))
    pos = [0] * N
    for i, p in enumerate(P):
        pos[p] = i

    ans = []

    def swap(x, y):
        if x > y:
            x, y = y, x
        P[x], P[y] = P[y], P[x]
        pos[P[x]] = x
        pos[P[y]] = y
        ans.append(x + 1)

    def F(L, R):
        if L == R:
            return True
        for x in range(L, R)[::-1]:
            if pos[x] < L or pos[x] >= R:
                return False
            while pos[x] < x:
                i = pos[x]
                swap(i, i+1)
        return True

    L = 0
    for R in range(N):
        if P[R] == R:
            if not F(L, R):
                print(-1)
                return
            L = R + 1
    if not F(L, N):
        print(-1)
        return

    print(len(ans))
    print(*ans)
    return


T = int(input())
for _ in range(T):
    main()