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 JavaScript (Node.js 12.16.1) (judge verdict: Time Limit Exceeded)

'use strict';

function Main(input) {
    const tmp = input.trim().split('\n');
    const N = Number(tmp[0]);
    const S = tmp[1];
    // console.log(N, S);

    let result = 0;
    for (let i = 0; i < N; i++) {
        for (let j = 1; j < N; j++) {
            for (let k = 1; k < N; k++) {
                if (j === k) continue;
                if (i + j + k > N - 1) break;
                const check1 = [S[i], S[i + j], S[i + j + k]];
                // console.log(`check1${check1}`);
                if (check(check1)) {
                    result++;
                }
                const check2 = [S[i], S[i + k], S[i + j + k]];
                // console.log(`check2${check2}`)
                if (check(check2)) {
                    result++;
                }
            }
        }
    }
    console.log(result / 2);
}
function check(arr) {
    if (arr[0] !== arr[1] && arr[0] !== arr[2] && arr[1] !== arr[2]) {
        return true;
    }
    return false;
}

Main(require('fs').readFileSync('/dev/stdin', 'utf8'));

// Main(`4
// RRGB`);
// Main(`39
// RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB`);