18748번 - Grp 스페셜 저지다국어

문제

Distribute all non-empty subsets of {a, b, c, . . .} (first n lowercase English letters) of size at most k into as few groups as possible, subject to the following conditions:

• each subset must belong to exactly one group;
• subsets belonging to the same group must have no common elements;
• the total size of subsets belonging to the same group must be at most k

입력

The only line contains two integers n and k (1 ≤ k ≤ n ≤ 17).

출력

Display the smallest number of groups g, followed by g group descriptions.

Group description i must consist of an integer s_i, followed by s_i subset descriptions. Each subset description must be a string containing subset elements in any order without spaces.

제한

힌트