Problem:
Score : 300 points

Problem Statement

A sequence a_1,a_2,... ,a_n is said to be /\/\/\/ when the following conditions are satisfied:

For each i = 1,2,..., n-2, a_i = a_{i+2}.

Exactly two different numbers appear in the sequence.

You are given a sequence v_1,v_2,...,v_n whose length is even.
We would like to make this sequence /\/\/\/ by replacing some of its elements.
Find the minimum number of elements that needs to be replaced.

Constraints

2 \leq n \leq 10^5

n is even.

1 \leq v_i \leq 10^5

v_i is an integer.

Input

Input is given from Standard Input in the following format:

n
v_1 v_2 ... v_n

Output

Print the minimum number of elements that needs to be replaced.

Sample Input 1

4
3 1 3 2

Sample Output 1

1

The sequence 3,1,3,2 is not /\/\/\/, but we can make it /\/\/\/ by replacing one of its elements: for example, replace the fourth element to make it 3,1,3,1.

Sample Input 2

6
105 119 105 119 105 119

Sample Output 2

0

The sequence 105,119,105,119,105,119 is /\/\/\/.

Sample Input 3

4
1 1 1 1

Sample Output 3

2

The elements of the sequence 1,1,1,1 are all the same, so it is not /\/\/\/.

Solution in Scala (2.11.7) (judge verdict: Wrong Answer)

object Main extends App {
  val sc = new java.util.Scanner(System.in)
  val n = sc.nextInt
  val v = List.fill(n)(sc.nextInt)
  var mOdd = Map(-1 -> 0)
  var mEven = Map(-1 -> 0)
  v.zipWithIndex.foreach{ case (x, idx) =>
    if (idx % 2 == 0) {
      mEven += x -> (mEven.getOrElse(x,0) + 1)
    } else {
      mOdd += x -> (mOdd.getOrElse(x,0) + 1)
    }
  }

  def cost(v1: Int, v2: Int): Int = {
    (n/2 - v1) + (n/2 - v2)
  }

  val mEvenSorted = mEven.toVector.sortBy(_._1).reverse
  val mOddSorted = mOdd.toVector.sortBy(_._1).reverse

  println((mEvenSorted(0), mOddSorted(0)) match { case ((e11,v11), (e12,v12)) =>
    if (e11 != e12) cost(v11,v12)
    else (mEvenSorted(1), mOddSorted(1)) match { case ((e21,v21), (e22,v22)) =>
      cost(v11,v22).min(cost(v12, v21))
    }
  })
}