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

namespace A
{
    class Program
    {
        static void Main(string[] args)
        {
            string line = Console.ReadLine();
            int N = int.Parse(line);
            line = Console.ReadLine();
            string[] strs = line.Split(' ');
            var listA = new List<int>();
            var listB = new List<int>();
            for (int i = 0; i < N; i++)
            {
                if (i % 2 == 0)
                {
                    listA.Add(int.Parse(strs[i]));
                }
                else
                {
                    listB.Add(int.Parse(strs[i]));
                }
            }
            listA.Sort();
            listB.Sort();

            var dictA = new Dictionary<int, int>();
            var dictB = new Dictionary<int, int>();
            int before = 0;
            int count = 0;
            for(int i = 0; i < listA.Count; i++)
            {
                if (before == listA[i])
                {
                    count++;
                }
                else
                {
                    if (count > 0) dictA.Add(before, count);
                    before = listA[i];
                    count = 1;
                }
            }
            if (count > 0) dictA.Add(before, count);

            before = 0;
            count = 0;
            for (int i = 0; i < listB.Count; i++)
            {
                if (before == listB[i])
                {
                    count++;
                }
                else
                {
                    if (count > 0) dictB.Add(before, count);
                    before = listB[i];
                    count = 1;
                }
            }
            if (count > 0) dictB.Add(before, count);

            

            var maxA = 0;
            var maxA_num = 0;
            var nextA = 0;
            var nextA_num = 0;
            var maxB = 0;
            var maxB_num = 0;
            var nextB = 0;
            var nextB_num = 0;

            foreach (var kvp in dictA.OrderBy(x => x.Value))
            {
                if (maxA <= kvp.Value)
                {
                    nextA = maxA;
                    nextA_num = maxA_num;
                    maxA = kvp.Value;
                    maxA_num = kvp.Key;
                }
            }
            foreach (var kvp in dictB.OrderBy(x => x.Value))
            {
                if (maxB <= kvp.Value)
                {
                    nextB = maxB;
                    nextB_num = maxB_num;
                    maxB = kvp.Value;
                    maxB_num = kvp.Key;
                }
            }

           if (maxA_num == maxB_num)
           {
                if (maxA + nextB < maxB + nextA)
                {
                    maxA = nextA;
                }
                else maxB = nextB;
           }
           Console.WriteLine(N - (maxA + maxB));
        }
    }
}