class Solution:

def minStickers(self, stickers, target):

cnt, res, n = collections.Counter(target), [float("inf")], len(target)

def dfs(dic, used, i):

if i == n:

res[0] = min(res[0], used)

elif dic[target[i]] >= cnt[target[i]]:

dfs(dic, used, i + 1)

elif used < res[0] - 1:

for sticker in stickers:

if target[i] in sticker:

for s in sticker:

dic[s] += 1

dfs(dic, used + 1, i + 1)

for s in sticker:

dic[s] -= 1

dfs(collections.defaultdict(int), 0, 0)

return res[0] < float("inf") and res[0] or -1