Problem: We have a string S of length N consisting of `R`, `G`, and `B`.  Find the number of triples (i,~j,~k)~(1 \leq i < j < k \leq N) that satisfy both of the following conditions:    * S_i \neq S_j, S_i \neq S_k, and S_j \neq S_k.   * j - i \neq k - j.

Submission attempts (in order):
def main():
    n = int(input())
    S = input()
    '''
    r_inds = []
    g_inds = []
    b_inds = []
    for i in range(len(S)):
        if S[i] == "R":
            r_inds.append(i)
        elif S[i] == "G":
            g_inds.append(i)
        else:
            b_inds.append(i)

    total_comb = len(r_inds)*len(g_inds)*len(b_inds)
    ded = 0
    for i in r_inds:
        for j in g_inds:
            s_ind = min(i, j)
            b_ind = max(i, j)
            diff = b_ind - s_ind
            bigger_ind = b_ind + diff
            smaller_ind = s_ind - diff
            if bigger_ind < len(S) and bigger_ind in b_inds:
                ded += 1
            if smaller_ind >= 0 and smaller_ind in b_inds:
                ded += 1
            if diff % 2 == 0:
                mid_diff = diff // 2
                mid_ind = s_ind + mid_diff
                if mid_ind in b_inds:
                    ded += 1
    print(total_comb - ded)
    '''
    color_num = defaultdict(int)
    num_subst = 0

    for i in range(len(S) - 1):
        color_num[S[i]] += 1 
        for j in range(i + 1, len(S)):
            if S[i] != S[j]:
                diff = j - i
                idx = j + diff
                if idx < len(S) and S[idx] != S[i] and S[idx] != S[j]:
                    num_subst += 1
    color_num[S[len(S) - 1]] += 1 
    total_num_comb = color_num["R"] * color_num["G"] * color_num["B"]
    print(total_num_comb - num_subst)

if __name__ == "__main__":
    main()


from collections import defaultdict


def main():
    n = int(input())
    S = input()
    '''
    r_inds = []
    g_inds = []
    b_inds = []
    for i in range(len(S)):
        if S[i] == "R":
            r_inds.append(i)
        elif S[i] == "G":
            g_inds.append(i)
        else:
            b_inds.append(i)

    total_comb = len(r_inds)*len(g_inds)*len(b_inds)
    ded = 0
    for i in r_inds:
        for j in g_inds:
            s_ind = min(i, j)
            b_ind = max(i, j)
            diff = b_ind - s_ind
            bigger_ind = b_ind + diff
            smaller_ind = s_ind - diff
            if bigger_ind < len(S) and bigger_ind in b_inds:
                ded += 1
            if smaller_ind >= 0 and smaller_ind in b_inds:
                ded += 1
            if diff % 2 == 0:
                mid_diff = diff // 2
                mid_ind = s_ind + mid_diff
                if mid_ind in b_inds:
                    ded += 1
    print(total_comb - ded)
    '''
    color_num = defaultdict(int)
    num_subst = 0

    for i in range(len(S) - 1):
        color_num[S[i]] += 1 
        for j in range(i + 1, len(S)):
            if S[i] != S[j]:
                diff = j - i
                idx = j + diff
                if idx < len(S) and S[idx] != S[i] and S[idx] != S[j]:
                    num_subst += 1
    color_num[S[len(S) - 1]] += 1 
    total_num_comb = color_num["R"] * color_num["G"] * color_num["B"]
    print(total_num_comb - num_subst)

if __name__ == "__main__":
    main()


Verdicts: Runtime Error

Accepted