ABREPEAT - Editorial

editorial
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41

Python code solution to this problem:

T=int(input())
for _ in range(T):
    N, K = map(int, input().split())
    word=input()
    b_count=0
    left_count=0
    right_count=0
    b_count=word.count("b")
    curr_b=0
    for x in range(N):
        if word[x] == "b":
            curr_b+=1
        elif word[x] == "a":
            left_count+=curr_b
            right_count+=(b_count-curr_b)
    res = K*(K+1)
    res = res//2
    res = res*(left_count+right_count)
    res-=K*left_count
    print(res)