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: Accepted)

import scala.io.{StdIn => in}
import scala.collection.{mutable => mu}

object Main extends App {
  import MapHelper._
  val n = in.readInt
  val seq = in.readLine.split(" ").map(_.toInt)

  val map1 = mu.HashMap.empty[Int,Int]
  val map2 = mu.HashMap.empty[Int,Int]
  for(i <- 0 until n) {
    if(i % 2 == 0) map1.addOrUpdate(seq(i), 1)
    else map2.addOrUpdate(seq(i), 1)
  }

  val max1 = map1.toIndexedSeq.sortBy(_._2)(Ordering[Int].reverse).take(2)
  val max2 = map2.toIndexedSeq.sortBy(_._2)(Ordering[Int].reverse).take(2)
  // println(max1.mkString(" "))
  // println(max2.mkString(" "))

  val res = (max1, max2) match {
    case (a, b) if a.head._1 != b.head._1 => a.head._2 + b.head._2
    case (a, b) if a.size == 2 && b.size == 2 => (a.head._2 + b.last._2) max (a.last._2 + b.head._2)
    case (a, b) if b.size == 2 => a.head._2 + b.last._2
    case (a, b) if a.size == 2 => a.last._2 + b.head._2
    case _ => n / 2
  }

  val ans = n - res
  println(ans)

  object MapHelper {
    implicit class AddOrUpdate[A](map:mu.HashMap[Int,Int]) {
      def addOrUpdate(key:Int, value:Int):mu.HashMap[Int,Int] =
      {
        if(map.contains(key)) map(key) += value
        else map += (key -> value)
        map
      }
    }
  }
}