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.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));

            return;
        }

        public void Solve(ConsoleInput cin)
        {

            var n = cin.ReadInt;
            var v = cin.ReadIntArray(n);

            bool fg = true;
            foreach(var elem in v)
            {
                if(elem != v[0])
                {
                    fg = false;
                }
            }
            Console.WriteLine(fg);
            if(fg)
            {
                Console.WriteLine(n / 2);
                return;
            }

            var evens = v.Where((ValueTuple, index) => index % 2 == 0).ToList();
            var odds = v.Where((ValueTuple, index) => index % 2 == 1).ToList();

            var evenMode = GetMode(evens);
            var oddMode = GetMode(odds);

            if (evenMode.first != oddMode.first)
            {
                int ans = 0;
                ans += GetDiff(evens, evenMode.first);
                ans += GetDiff(odds, oddMode.first);
                Console.WriteLine(ans);
                return;
            }
            else
            {
                int ans1 = 0;
                int ans2 = 0;

                ans1 += GetDiff(evens, evenMode.first);
                ans1 += GetDiff(odds, oddMode.second);
                
                ans2 += GetDiff(evens, evenMode.second);
                ans2 += GetDiff(odds, oddMode.first);

                Console.WriteLine(Min(ans1, ans2));
                return;
            }

        }
        public class MyMode
        {
            public int first {get; set;}
            public int second {get; set;}
        }
        public MyMode GetMode(List<int> numList)
        {
            var dict = new Dictionary<int, int>();
            foreach(var elem in numList)
            {
                if(!dict.ContainsKey(elem))
                {
                    dict.Add(elem, 1);
                }
                else
                {
                    dict[elem]++;
                }
            }
            var orderedDict= dict.OrderByDescending((x) => x.Value).ToList();
            var myMode = new MyMode();
            if (orderedDict.Count == 1)
            {
                myMode.first = orderedDict[0].Key;
                myMode.second = orderedDict[0].Key;
            }
            else
            {
                myMode.first = orderedDict[0].Key;
                myMode.second = orderedDict[1].Key;
            }
            return myMode;

        }
        public int GetDiff(List<int> original, int mode)
        {
            int count = 0;
            foreach(var elem in original)
            {
                if (elem != mode)
                {
                    count++;
                }
            }
            return count;
        }

    }

    public static class Extensions
    {
        public static string Reverse(this string sourse)
        {
            char[] chrAry = sourse.ToCharArray();
            Array.Reverse(chrAry);
            return new string(chrAry);
        }
    }

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }
}