java 代码实现 M个数组每个数组抽出一个值组成长度为N的字符共有多少种可能,
比如 String[] m1 ={'a','b','c'},String[] m2={'d','e'},String[] m3={'y','u','w'},
N的长度为2 那么结果又 a-d a-e a-y a-u a-w b-d b-e b-y b-u b-w c-d c-e c-y c-u c-w d-y d-u d-w e-y e-u e-w
N的长度为3 那么结果又 a-d-y a-d-u a-d-w a-e-y a-e-u a-e-w b-d-y b-d-u b-d-w b-e-y b-d-u b-d-w c-d-y c-d-u c-d-w c-e-y c-e-u c-e-w