Little Elephant and Filling

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A Little Elephant from the Zoo of Lviv likes lucky strings, i.e., the strings that consist only of the lucky digits 4 and 7.
The Little Elephant has the string S such that each character in S is either the lucky digit (4 or 7) or the question mark ?. He can replace each question mark with one of the lucky digits in order to obtain the lucky string. He wants to know the number of different ways he can do this such that the resulting lucky string has no more than K different substrings. Help him and find this number. Note, that he need to replace all question marks.
Consider some example. From the string 47?4? we can obtain four lucky strings by replacing question marks with the lucky digits: 47444, 47447, 47744 and 47747. The corresponding numbers of different substrings are 11, 11, 12 and 11. For example, all different substrings of the string 47447 are 4, 7, 44, 47, 74, 447, 474, 744, 4744, 7447 and 47447.
Notes.
Let S be some lucky string. Then
 S denotes the length of the string S;
 S[i] (1 ≤ i ≤ S) denotes the i^{th} character of S (the numeration of characters starts from 1);
 The string T of the length M is called a substring of S if for some k from 0 to S  M we have
T[1] = S[k + 1], T[2] = S[k + 2], ..., T[M] = S[k + M].
Input
The first line of the input file contains a single positive integer T, the number of test cases. T test cases follow. The first line of each test case contains two space separated integers N and K. The second line contains the string S of the length N.
Output
For each test case output a single line containing the answer for the corresponding test case.
Constraints
1 ≤ T ≤ 4747
1 ≤ N, K ≤ 50
For each string S from the input file we have that S = N and each character in S is either the lucky digit (4 or 7) or the question mark ?.
Example
Input: 2 2 2 ?? 3 7 ?4? Output: 2 4
Author:  witua 
Tester:  anton_lunyov 
Editorial  http://discuss.codechef.com/problems/LUCKFILL 
Tags  cook22 medium witua 
Date Added:  27012012 
Time Limit:  2 sec 
Source Limit:  50000 Bytes 
Languages:  ADA, ASM, BASH, BF, C, C99 strict, CAML, CLOJ, CLPS, CPP 4.3.2, CPP 4.9.2, CPP14, CS2, D, ERL, FORT, FS, GO, HASK, ICK, ICON, JAVA, JS, LISP clisp, LISP sbcl, LUA, NEM, NICE, NODEJS, PAS fpc, PAS gpc, PERL, PERL6, PHP, PIKE, PRLG, PYTH, PYTH 3.1.2, RUBY, SCALA, SCM guile, SCM qobi, ST, TCL, TEXT, WSPC 
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SUCCESSFUL SUBMISSIONS
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@dawnavs 447 = S[3,5] and
@saroj T is the number of
@admin, would u mind
@abhiuppar Note that each
this problem is still not in
@saroj: The problem is there
@saroj: The problem is there in practice section. Please check here: http://www.codechef.com/problems/LUCKFILL
@saroj: You can only submit
@saroj: You can only submit for a problem in a contest untill it is running. After the end of he contest the problem will be moved to practice section. you can check them here: http://www.codechef.com/problems/medium.