Colorful Subsequence

AtCoder

IDagc031_a

Time2000ms

Memory256MB

Difficulty—

You are given a string $S$ of length $N$. Among its subsequences, count the ones such that all characters are different, modulo $10^9+7$. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings. Here, a subsequence of a string is a concatenation of **one or more** characters from the string without changing the order. ## Constraints * $1 \leq N \leq 100000$ * $S$ consists of lowercase English letters. * $|S|=N$ ## Input Input is given from Standard Input in the following format: $N$ $S$ [samples]

Samples

Input #1

4
abcd

Output #1

15

Since all characters in $S$ itself are different, all its subsequences satisfy the condition.

Input #2

3
baa

Output #2

5

The answer is five: `b`, two occurrences of `a`, two occurrences of `ba`. Note that we do not count `baa`, since it contains two `a`s.

Input #3

5
abcab

Output #3

API Response (JSON)

{
  "problem": {
    "name": "Colorful Subsequence",
    "description": {
      "content": "You are given a string $S$ of length $N$. Among its subsequences, count the ones such that all characters are different, modulo $10^9+7$. Two subsequences are considered different if their characters ",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "agc031_a"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "You are given a string $S$ of length $N$. Among its subsequences, count the ones such that all characters are different, modulo $10^9+7$. Two subsequences are considered different if their characters ...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments