A15097. Black and White Stripe

You have a stripe of checkered paper of length $n$ . Each cell is either white or black.

What is the minimum number of cells that must be recolored from white to black in order to have a segment of $k$ consecutive black cells on the stripe?

If the input data is such that a segment of $k$ consecutive black cells already exists, then print 0.

The first line contains an integer $t$ ( $1 \le t \le 10^4$ ) — the number of test cases.

Next, descriptions of $t$ test cases follow.

The first line of the input contains two integers $n$ and $k$ ( $1 \le k \le n \le 2\cdot10^5$ ). The second line consists of the letters 'W' (white) and 'B' (black). The line length is $n$ .

It is guaranteed that the sum of values $n$ does not exceed $2\cdot10^5$ .

For each of $t$ test cases print an integer — the minimum number of cells that need to be repainted from white to black in order to have a segment of $k$ consecutive black cells.

In the first test case, $s$ ="BBWBW" and $k=3$ . It is enough to recolor $s_3$ and get $s$ ="BBBBW". This string contains a segment of length $k=3$ consisting of the letters 'B'.

In the second test case of the example $s$ ="BBWBW" and $k=5$ . It is enough to recolor $s_3$ and $s_5$ and get $s$ ="BBBBB". This string contains a segment of length $k=5$ consisting of the letters 'B'.

In the third test case of the example $s$ ="BBWBW" and $k=1$ . The string $s$ already contains a segment of length $k=1$ consisting of the letters 'B'.