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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System.Linq;
using System.Collections.Generic;
using System;

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        var d = new Dictionary<int, int>();
        var d2 = new Dictionary<int, int>();
        for (int i = 0; i < n; i += 2)
        {
            if (d2.ContainsKey(a[i])) d2[a[i]]++;
            else d2[a[i]] = 1;
        }
        for (int i = 1; i < n; i += 2)
        {
            if (d.ContainsKey(a[i])) d[a[i]]++;
            else d[a[i]] = 1;
        }
        var ans = new List<int>();
        var dr = d.OrderByDescending(x => x.Value).ToArray();
        var d2r = d2.OrderByDescending(x => x.Value).ToArray();
        if (dr.Length == 1 && d2r.Length == 1 && dr[0].Key != d2r[0].Key)
        { Console.WriteLine(0); goto end; }
        if (dr.Length == 1 && d2r.Length == 1 && dr[0].Key == d2r[0].Key)
        { Console.WriteLine(n / 2); goto end; }
        if (dr.Length == 1 && d2r.Length > 1)
        {
            if (dr[0].Key != d2r[0].Key) { Console.WriteLine(n / 2 - d2r[0].Value); goto end; }
            else if (dr[0].Key != d2r[1].Key) { Console.WriteLine(n / 2 - d2r[1].Value); goto end; }
        }
        if (dr.Length > 1 && d2r.Length == 1)
        {
            if (d2r[0].Key != dr[0].Key) { Console.WriteLine(n / 2 - dr[0].Value); goto end; }
            else if (d2r[0].Key != dr[1].Key) { Console.WriteLine(n / 2 - dr[1].Value); goto end; }
        }
        if (dr[0].Key != d2r[0].Key) ans.Add(n - dr[0].Value - d2r[0].Value);
        if (dr[0].Key != d2r[1].Key) ans.Add(n - dr[0].Value - d2r[1].Value);
        if (dr[1].Key != d2r[0].Key) ans.Add(n - dr[1].Value - d2r[0].Value);
        if (dr[1].Key != d2r[1].Key) ans.Add(n - dr[1].Value - d2r[1].Value);
        Console.WriteLine(ans.Min());
        end:;
    }

}