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 Java (OpenJDK 11.0.6) (judge verdict: Time Limit Exceeded)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);
        int a = stdIn.nextInt() ;
        String S = stdIn.next();
        char C1,C2,C3 ;
        int count = 0;

        for (int i = 0; i < a; i++) {
            C1 = S.charAt(i) ;
            for (int j = i+1; j <a; j++) {
                C2 = S.charAt(j);
                if(C1 == C2) ;
                else{
                    for (int k = j+1; k <a; k++) {
                        //  System.out.println(i+" "+j+" "+k);
                        C3 = S.charAt(k);
                        if( C2 == C3 || C1 == C3);
                        else if(j-i == k-j ) ;
                        else {
                            count++ ;
                        }
                        // System.out.println("GET " +i+" "+j+" "+k);
                    }
                }
            }
        }

        System.out.println(count);
    }
}