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: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Main
{
    class Program
    {
        static void Main(string[] arg)
        {
            int n = int.Parse(Console.ReadLine());
            var vLine = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            int count = 0;
            var vline1 = new List<int>();
            var vline2 = new List<int>();
            var set1 = new HashSet<int>();
            var set2 = new HashSet<int>();
            for (int i = 0; i < n - 2; i++)
            {
                int v1 = vLine[i];
                int v2 = vLine[i + 2];
                if(i%2 == 1)
                {
                    vline1.Add(v1);
                    set1.Add(v1);
                }
                else
                {
                    vline2.Add(vLine[i]);
                    set2.Add(vLine[i]);

                }

                if (v1 != v2)
                {
                    count++;
                }
                
                
            }
            vline1.Add(vLine[vLine.Length - 2]);
            vline2.Add(vLine[vLine.Length - 1]);
            set1.Add(vLine[vLine.Length - 2]);
            set2.Add(vLine[vLine.Length - 1]);

            if (set1.Count == 1 && set2.Count == 1 && (vline1[0] != vline2[0]))
            {
                Console.WriteLine(count);
            }
            else
            {

                int c1 = int.MaxValue;
                int c2 = int.MaxValue;
                foreach (int i in set1)
                {
                    int c = vline1.Count(x => x == i);
                    
                    if (c1 > c)
                    {
                        c1 = c;
                    }
                }
                foreach (int i in set2)
                {
                    int c = vline2.Count(x => x == i);
                    if (c2 > c)
                    {
                        c2 = c;
                    }
                }
                count += c1 > c2 ? c2 : c1;

                Console.WriteLine(count);
                
            }
            Console.ReadLine();

        }
    }
}