Keys and Doors
A grid maze contains your start @, walls #, keys a-f and matching doors A-F (a door needs its key). Print the fewest steps to collect ALL keys, or −1.
Input: the first line has N and M; the next N lines are the maze.
Output: the minimum steps to hold every key, or −1.
Constraints:
- 1 ≤ N, M ≤ 100
- at most 6 keys
Sample Tests
Input 1
3 4 @a.A .... ....
Output 1
1
Input 2
1 3 @#a
Output 2
-1
Discussion (opens after you solve — no spoilers before)
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