Остров после дождя

def water_volume(island, a, b):
    result = 0

    max_height = max([height for row in island for height in row])

    rained_island = []

    for i in range(a):
        rained_island.append([])

        for j in range(b):
            if i == 0 or i == a - 1 or j == 0 or j == b - 1:
                rained_island[i].append(island[i][j])
            else:
                rained_island[i].append(max_height)

    is_changed = True

    while is_changed:
        is_changed = False

        for i in range(1, a - 1):
            for j in range(1, b - 1):
                min_height = min(rained_island[i - 1][j], rained_island[i][j - 1], rained_island[i][j + 1], rained_island[i + 1][j])

                if rained_island[i][j] > min_height and rained_island[i][j] != island[i][j]:
                     rained_island[i][j] = min_height if min_height > island[i][j] else island[i][j]
                     is_changed = True

    for i in range(a):
        for j in range(b):
            result += rained_island[i][j] - island[i][j]

    return result

K = int(input())
results = []

for i in range(K):
    island = []
    N, M = (int(p) for p in input().split())

    for j in range(N):
        island.append([int(p) for p in input().split()])

    results.append(water_volume(island, N, M))

for x in results:
    print(x)