Problem:
Score : 500 points

Problem Statement

There are N boxes arranged in a circle. The i-th box contains A_i stones.

Determine whether it is possible to remove all the stones from the boxes by repeatedly performing the following operation:

Select one box. Let the box be the i-th box. Then, for each j from 1 through N, remove exactly j stones from the (i+j)-th box. Here, the (N+k)-th box is identified with the k-th box.

Note that the operation cannot be performed if there is a box that does not contain enough number of stones to be removed.

Constraints

1 ≦ N ≦ 10^5

1 ≦ A_i ≦ 10^9

Input

The input is given from Standard Input in the following format:

N
A_1 A_2 … A_N

Output

If it is possible to remove all the stones from the boxes, print YES. Otherwise, print NO.

Sample Input 1

5
4 5 1 2 3

Sample Output 1

YES

All the stones can be removed in one operation by selecting the second box.

Sample Input 2

5
6 9 12 10 8

Sample Output 2

YES

Sample Input 3

4
1 2 3 1

Sample Output 3

NO

Solution in Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner

/**
 * Created by sonetsuyoshi on 2015/12/16.
 */

object Main extends App {
  val sc = new Scanner(System.in)
  val n = sc.nextInt
  val a = Array.fill(n)(sc.nextLong)

  run()

  def run(): Unit = {
    val s = a.sum
    val c = n.toLong * (n + 1) / 2

    if(s % c != 0) {
      println("NO")
      return
    }

    val k = s / c

    val d = for(i <- 0 until n) yield a((i + 1) % n) - a(i)

    if(d.exists(x => x > k || (k - x) % n != 0)) println("NO")
    else println("YES")
  }
}