http://poj.org/problem?id=2157
Acm, a treasure-explorer, is exploring again. This time he is in a special maze, in which there are some doors (at most 5 doors, represented by 'A', 'B', 'C', 'D', 'E' respectively). In order to find the treasure, Acm may need to open doors. However, to open a door he needs to find all the door's keys (at least one) in the maze first. For example, if there are 3 keys of Door A, to open the door he should find all the 3 keys first (that's three 'a's which denote the keys of 'A' in the maze). Now make a program to tell Acm whether he can find the treasure or not. Notice that Acm can only go up, down, left and right in the maze.
Input
The input consists of multiple test cases. The first line of each test case contains two integers M and N (1 < N, M < 20), which denote the size of the maze. The next M lines give the maze layout, with each line containing N characters. A character is one of the following: 'X' (a block of wall, which the explorer cannot enter), '.' (an empty block), 'S' (the start point of Acm), 'G' (the position of treasure), 'A', 'B', 'C', 'D', 'E' (the doors), 'a', 'b', 'c', 'd', 'e' (the keys of the doors). The input is terminated with two 0's. This test case should not be processed.
Output
For each test case, in one line output "YES" if Acm can find the treasure, or "NO" otherwise.
Sample Input
4 4 S.X. a.X. ..XG .... 3 4 S.Xa .aXB b.AG 0 0
Sample Output
YES NO
先找小写字母，标记每种小写原来总共的exsit[], 能过搜到的小写字母用f[]标记，搜到一个，就加一，如果搜到的是大写字母，判断f[]>exsit[] 如果是，入队，如果不是，先保存起来，之后每次判断一下，如果满足f[]>exsit[]就入队。如果搜到‘G’结束搜索，得出答案。
