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A substring of a string is a contiguous sequence of characters from the string. For example, BC
is a substring of ABCD
which starts from the second character of ABCD
. Another example, ABC
is a substring of ABCD
which starts from the first character of ABCD
. Note that ABCD
itself is also a substring of ABCD
.
In this problem, we define a special substring as a non-empty substring that contains only the same character. For example, B
and CC
are special substrings of ABBCCC
, while ABBC
and BC
are not special substrings.
You are given a string S of length N and an integer K. Your task is to determine the minimum number of characters of S that need to be changed such that there exists a special substring of length K in S.
For example, let N = 6, K = 4, and S = ABBCCC
. In this example, we only need to change the third character of S to C (i.e. ABBCCC
→ ABCCCC
) so that we have a special substring CCCC
of length 4.
Input begins with a line containing two integers: N K (1 ≤ K ≤ N ≤ 100 000) representing the length of the string and the length of a special substring that should be produced, respectively. The next line contains a string S containing N uppercase alphabetical character, i.e. Si ∈ [A-Z
].
Output in a line an integer representing the minimum number of characters of S that need to be changed such that there exists a special substring of length K in the given S.
6 4 ABBCCC
1
9 6 AABCABBBA
2
If we change the fourth and fifth characters of S to B, i.e. AABCABBBA
→ AABBBBBBA
, then S will have a special substring of length 6 which is BBBBBB
(AABBBBBBA
). In this case, it is not possible to have a special substring of length 6 in S by changing fewer than 2 characters.
10 7 BAABAABAAB
2
If we change the fourth and seventh characters of S to A, i.e. BAABAABAAB
→ BAAAAAAAAB
, then S will have a special substring of length 7 which is AAAAAAA
(either BAAAAAAAAB
or BAAAAAAAAB
). In this case, it is not possible to have a special substring of length 7 in S by changing fewer than 2 characters.
6 2 INNCCC
0
The string INNCCC
already has a special substring of length 2, e.g., NN
or CC
.
ICPC > Regionals > Asia Pacific > Indonesia > Indonesia National Contest > INC 2020 F번