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 a = sc.nextInt();
		
		String s = sc.next();
        int ans = 0;
        int r = 0;
        int g = 0;
        int b = 0;
        for(int i=0;i<a;i++){if(s.charAt(i)=='R'){r++;}
                             if(s.charAt(i)=='G'){g++;}
                             if(s.charAt(i)=='B'){b++;}
                            }
        int dr = r;
        int dg = g;
        int db = b;
        if(a>3){for(int i=0;i<a-3;i++){if(s.charAt(i)=='R'){r--;}if(s.charAt(i)=='G'){g--;}if(s.charAt(i)=='B'){b--;}
                                       dr = r;dg = g; db = b;
               for(int j=i+1;j<a-1;j++){if(s.charAt(i)=='R'){
                 if(s.charAt(j)=='G'){ans+=db;if(2*j-i<a && s.charAt(2*j-i)=='B'){ans--;}dg--;}
               if(s.charAt(j)=='B'){ans+=dg;if(2*j-i<a && s.charAt(2*j-i)=='G'){ans--;}db--;}
               if(s.charAt(j)=='R'){dr--;}                                             
                                                            }
                                        if(s.charAt(i)=='G'){
                 if(s.charAt(j)=='R'){ans+=db;if(2*j-i<a && s.charAt(2*j-i)=='B'){ans--;}dr--;}
               if(s.charAt(j)=='B'){ans+=dr;if(2*j-i<a && s.charAt(2*j-i)=='R'){ans--;}db--;}
               if(s.charAt(j)=='G'){dg--;}                           
                                                            } 
                              
                                       if(s.charAt(i)=='B'){
                 if(s.charAt(j)=='G'){ans+=dr;if(2*j-i<a && s.charAt(2*j-i)=='R'){ans--;}dg--;}
               if(s.charAt(j)=='R'){ans+=dg;if(2*j-i<a && s.charAt(2*j-i)=='G'){ans--;}dr--;}
               if(s.charAt(j)=='B'){db--;}                                                    
                                                           } 
                                       }                               
                                      }                           
              }
       
		System.out.println(ans);
	}
}