Problem:
Score : 400 points

Problem Statement

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.

Constraints

1 \leq N \leq 4000

S is a string of length N consisting of R, G, and B.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of triplets in question.

Sample Input 1

4
RRGB

Sample Output 1

1

Only the triplet (1,~3,~4) satisfies both conditions. The triplet (2,~3,~4) satisfies the first condition but not the second, so it does not count.

Sample Input 2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2

1800

Solution in C++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < n; ++i)
#define ll long long
#define P pair<int,int>
#define fast_io ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
const int MOD = 1000000007;
const int INF = 2002002002;
const ll LLINF = 9009009009009009009;
using namespace std;

int main() {
    fast_io
    string s;
    int n;
    cin >> n >> s;
    map<char,int> mp;
    rep(i,n) {
        mp[s[i]]++;
    }
    int count = 0;
    rep(i,n) {
        int c = i;
        rep(j,n) {
            int l = i-j;
            int r = i+j;
            if (l < 0 || r > n-1) break;
            if (s[c] != s[l] && s[l] != s[r] && s[r] != s[c]) count++;
        }
    }
    cout << ((mp['R'] * mp['G'] * mp['B']) - count) << endl;
    return 0;
}