Problem:
Score : 200 points

Problem Statement

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

Output

Print YES if you can sort p in ascending order in the way stated in the problem statement, and NO otherwise.

Sample Input 1

5
5 2 3 4 1

Sample Output 1

YES

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

Sample Input 2

5
2 4 3 5 1

Sample Output 2

NO

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

Sample Input 3

7
1 2 3 4 5 6 7

Sample Output 3

YES

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

Solution in Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
    val a = sc.nextLine().toInt()
    val b = sc.nextLine().split(" ").map { it.toInt() }
    println(problem135_b(a, b))
}

fun problem135_b(a: Int, b: List<Int>): String {
    val list = b.toMutableList()

    var swapCount = 0

    for (i in 1..b.size) {

        // 間違っている場合入れ替えを行う
        if (list[i - 1] != i) {

            if (swapCount > 0) {
                return "NO"
            }

            val tmpA = list[i - 1]
            list[i - 1] = list[tmpA - 1]    // 左側の値を正しいものに
            list[tmpA - 1] = tmpA
            swapCount++

        }
    }
    return "YES"
}