0 or 1 Swap

AtCoder

IDabc135_b

Time2000ms

Memory256MB

Difficulty—

We have a sequence $p$ = {$p_1,\ p_2,\ ...,\ p_N$} which is a permutation of {$1,\ 2,\ ...,\ N$}. You can perform the following operation at most once: choose integers $i$ and $j$ $(1 \leq i < j \leq N)$, and swap $p_i$ and $p_j$. Note that you can also choose not to perform it. Print `YES` if you can sort $p$ in ascending order in this way, and `NO` otherwise. ## Constraints * All values in input are integers. * $2 \leq N \leq 50$ * $p$ is a permutation of {$1,\ 2,\ ...,\ N$}. ## Input Input is given from Standard Input in the following format: $N$ $p_1$ $p_2$ $...$ $p_N$ [samples]

Samples

Input #1

5
5 2 3 4 1

Output #1

YES

You can sort $p$ in ascending order by swapping $p_1$ and $p_5$.

Input #2

5
2 4 3 5 1

Output #2

NO

In this case, swapping any two elements does not sort $p$ in ascending order.

Input #3

7
1 2 3 4 5 6 7

Output #3

YES

$p$ is already sorted in ascending order, so no operation is needed.

API Response (JSON)

{
  "problem": {
    "name": "0 or 1 Swap",
    "description": {
      "content": "We have a sequence $p$ = {$p_1,\\ p_2,\\ ...,\\ p_N$} which is a permutation of {$1,\\ 2,\\ ...,\\ N$}. You can perform the following operation at most once: choose integers $i$ and $j$ $(1 \\leq i < j \\leq ",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc135_b"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "We have a sequence $p$ = {$p_1,\\ p_2,\\ ...,\\ p_N$} which is a permutation of {$1,\\ 2,\\ ...,\\ N$}.\nYou can perform the following operation at most once: choose integers $i$ and $j$ $(1 \\leq i < j \\leq ...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

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