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 Kotlin (1.3.71) (judge verdict: Wrong Answer)

import java.util.*

fun main(args: Array<String>) {
    val n = readLine()!!.toInt()
    val s = readLine()!!

    val r = IntArray(n){-1}
    val g = IntArray(n){-1}
    val b = IntArray(n){-1}

    var answer = 0L

    var rcnt = 0
    var gcnt = 0
    var bcnt = 0
    repeat(n) {
        when {
            s[it] == 'R' -> {
                r[rcnt] = it
                rcnt++
            }
            s[it] == 'G' -> {
                g[gcnt] = it
                gcnt++
            }
            s[it] == 'B' -> {
                b[bcnt] = it
                bcnt++
            }
        }
    }

    repeat(rcnt) {rr->
        repeat(gcnt) {gg->
            repeat(bcnt) { bb ->
                if (Math.abs(g[gg] - r[rr]) != Math.abs(b[bb] - g[gg]) 
                    && Math.abs(g[gg] - r[rr]) != Math.abs(b[bb] - r[rr])
                    && Math.abs(b[gg] - g[rr]) != Math.abs(b[bb] - r[rr])) {
                    answer++
                }
            }
        }
    }
    println(answer)
}