B'You have a string a and a string b . Both of the strings have length n . There are at most 10 different characters in the string a . You also have a set Q . Initially, the set Q is empty. You can apply the following operation on the string a any number of times: For example, Let the string a be " tt{abecca} ". We can do the following operations: You can apply any number of operations on a , but in the end, the set Q should contain at most k different characters. Under this constraint, you have to maximize the number of integer pairs (l, r) ( 1 <= q l <= q r <= q n ) such that a[l,r] = b[l,r] . Here, s[l,r] means the substring of string s starting at index l (inclusively) and ending at index r (inclusively). Each test contains multiple test cases. The first line contains the number of test cases t ( 1 <= t <= 10^4 ). The description of the test cases follows. The first line contains two integers n and k ( 1 <= q n <= q 10^5 , 0 <= q k <= q 10 ) -- the length of the two strings and the limit on different characters in the set Q . The second line contains the string a of length n . There is at most 10 different characters in the string a . The last line contains the string b of length n . Both of the strings a and b contain only lowercase English letters. The sum of n over all test cases doesn 't exceed 10^5 . For each test case, print a single integer in a line, the maximum number of pairs (l, r) satisfying the constraints. In the first case, we can select index i = 3 and replace it with character c = tt{d} . All possible pairs (l,r) will be valid. In the second case, we can 't perform any operation. The 3 valid pairs (l,r) are: In the third case, we can choose index 2 and index 3 and replace them with the char'...