RGB Triplets

AtCoder

IDabc162_d

Time2000ms

Memory256MB

Difficulty—

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: $N$ $S$ [samples]

Samples

Input #1

4
RRGB

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.

Input #2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Output #2

API Response (JSON)

{
  "problem": {
    "name": "RGB Triplets",
    "description": {
      "content": "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: *   $S_i \\neq S_j$,",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc162_d"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "We have a string $S$ of length $N$ consisting of `R`, `G`, and `B`.\nFind the number of triples $(i,~j,~k)~(1 \\leq i < j < k \\leq N)$ that satisfy both of the following conditions:\n\n*   $S_i \\neq S_j$,...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments