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 sc = Scanner(System.`in`)
    val n = sc.nextInt()
    val s = sc.next()
    println(problem162d(n, s))
}

fun problem162d(n: Int, s: String): Int {

    val rs = IntArray(n + 1) { 0 }
    for (i in 0 until n) {
        rs[i + 1] = rs[i] + if (s[i] == 'R') 1 else 0
    }
    val gs = IntArray(n + 1) { 0 }
    for (i in 0 until n) {
        gs[i + 1] = gs[i] + if (s[i] == 'G') 1 else 0
    }
    val bs = IntArray(n + 1) { 0 }
    for (i in 0 until n) {
        bs[i + 1] = bs[i] + if (s[i] == 'B') 1 else 0
    }
    val all = rs.last() * gs.last() * bs.last()
    var sub = 0;
    for (i in 0 until n) {
        for (j in i + 1 until n) {
            if (s[i] == s[j]) continue
            val k = j * 2 - i
            if (k >= n || s[k] == s[i] || s[k] == s[j]) continue
            sub++
        }
    }

    return all - sub
}