Topcoder SRM 689 NonDeterministicSubstring

this problem is about

Problem Statement
	You are given two Strings: A and B. Each character in A is either '0' or '1'. Each character in B is '0', '1', or '?'. A string C matches B if we can change B into C by changing each '?' in B either to '0' or to '1'. Different occurrences of '?' may be changed to different digits. For example, C = "0101" matches B = "01??". Note that each character in C must be either '0' or '1', there cannot be any '?' remaining. Consider all possible strings that match B. How many of these strings occur as a (contiguous) substring in A? Compute and return their number. Note that we only count each good string once, even if it has multiple occurrences in A.
Definition
	Class: NonDeterministicSubstring Method: ways Parameters: String, String Returns: long Method signature: long ways(String A, String B) (be sure your method is public)
Limits
	Time limit (s): 2.000 Memory limit (MB): 256 Stack limit (MB): 256
Constraints
-	A will contain between 1 and 50 characters, inclusive.
-	B will contain between 1 and 50 characters, inclusive.
-	Each character in A will be '0' or '1'.
-	Each character in B will be '0', '1' or '?'.
Examples
0)
	"00010001" "??" Returns: 3 There are four strings that match B: the strings "00", "01", "10", and "11". Out of these, the string "11" does not occur in A as a substring. The other three do occur, hence the answer is 3.
1)
	"00000000" "??0??0" Returns: 1 There are 16 different strings that match B, but out of those only the string "000000" is a substring of A.
2)
	"001010101100010111010" "???" Returns: 8 Each of the 8 strings that match B occurs somewhere in A.
3)
	"00101" "??????" Returns: 0 Here, the length of B is greater than the length of A. Clearly, a string that matches this B cannot be a substring of this A.
4)
	"1101010101111010101011111111110001010101" "???????????????????????????????????" Returns: 6

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My approach


1. A>B and
2. Find B length
3. Make all possible String with length of B and push HashSet
4. HashSet will filter duplication.
5. and finally only unique strings remain in hashset
6. compare all string with B if index of character is not ?
7. count all if it is match


my code is below

public long ways(String A, String B){
  HashSet<String> set = new HashSet<String>();
  
  int blen = B.length();
  for (int i = 0; i <= A.length()-blen; i++) {
   set.add(A.substring(i, i+blen));
  }
  
  Iterator<String> iter =  set.iterator();
  int count =0;
  while (iter.hasNext()) {
   String str = iter.next();
   boolean found = true;   
   for (int i = 0; i < blen; i++) {
    if(B.charAt(i)!= '?'){
     if(A.charAt(i) != B.charAt(i)){
      found =false;
      break;
     }
    }
   }
   if(found){
    count++;
   }
  }
  return count;
 }