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: Wrong Answer)

import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
  	int n=sc.nextInt(),r=0,b=0,g=0;
    String[] s=sc.next().split("");
    for(int i=0;i<n;i++){
      if(s[i].equals("R")){
        r++;
      }else if(s[i].equals("B")){
        b++;
      }else{
        g++;
      }
    }
    int f=r*g*b;
    for(int i=0;i<n;i++){
      for(int j=i+1;j<n;j++){
        if(n-1>=(2*j-i)){
          if(s[i].equals(s[j])==false&&s[j].equals(s[2*j-i])==false&&s[2*j-i].equals(s[i])==false){
            f=f-1;
          }
        }
      }
    }
    System.out.print(f);
  }
}