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++14 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

struct numAndCnt {
  int num;
  int cnt;
};

int main()
{
  int n;
  vector<int> evenSeries;  //偶数部
  vector<int> oddSeries; //奇数部
  vector<int> sortedEvenSeries; //偶数部の昇順ソート(重複要素削除)
  vector<int> sortedOddSeries; //奇数部の昇順ソート(重複要素削除)
  
  /* Input */
  cin >> n;

  for (int id = 0; id < n; id++) {
    int val;
    cin >> val;

    if (id % 2 == 0) {
      evenSeries.push_back(val);
      sortedEvenSeries.push_back(val);
    }
    else
    {
      oddSeries.push_back(val);
      sortedOddSeries.push_back(val);
    }
  }

  // Research most numberous from evenSeries and oddSeries. ----------------

  /* Create List of num and count. */
  vector<numAndCnt> evenMax;
  int evenMaxCount = 0;
  for (int id = 0; id < evenSeries.size(); id++) {
    numAndCnt tempIns;
    tempIns.num = evenSeries[id];
    tempIns.cnt = count(evenSeries.begin(), evenSeries.end(), evenSeries[id]);
    evenMax.push_back(tempIns);
  }
  vector<numAndCnt> oddMax;
  int oddMaxCount = 0;
  for (int id = 0; id < oddSeries.size(); id++) {
    numAndCnt tempIns;
    tempIns.num = oddSeries[id];
    tempIns.cnt = count(oddSeries.begin(), oddSeries.end(), oddSeries[id]);
    oddMax.push_back(tempIns);
  }

  /* Sort numAndCnt's instance using value of count. */
  sort(evenMax.begin(), evenMax.end(), [](const numAndCnt &c, const numAndCnt &d) {return c.cnt > d.cnt; });
  sort(oddMax.begin(), oddMax.end(), [](const numAndCnt &c, const numAndCnt &d) {return c.cnt > d.cnt; });

  /* Erase numAndCnt's instance using value of number. */
  {
    auto it = evenMax.begin();
    while (it != evenMax.end() - 1)
    {
      if ((*it).num == (*(it + 1)).num) //If current number equal next number, erase current number.
        it = evenMax.erase(it);
      else
        it++;
    }
  }
  {
    auto it = oddMax.begin();
    while (it != oddMax.end() - 1)
    {
      if ((*it).num == (*(it + 1)).num) //If current number equal next number, erase current number.
        it = oddMax.erase(it);
      else
        it++;
    }
  }

  if (evenMax.size() == 1 && oddMax.size() > 1) {
    cout << n / 2 - oddMax[0].cnt << endl;
  }
  else if (oddMax.size() == 1 && evenMax.size() > 1) {
    cout << n / 2 - evenMax[0].cnt << endl;
  }
  else if (oddMax.size() == 1 && evenMax.size() == 1) {
    if (oddMax[0].num == evenMax[0].num)
      cout << n / 2 << endl;
    else
      cout << 0 << endl;
  }
  else {  //重複要素をeraseしたvectorの要素数が1より大きければこちら
    if (evenMax[0].num == oddMax[0].num) {
      if (evenMax[1].num > oddMax[1].num) {
        cout << n - (evenMax[1].cnt + oddMax[0].cnt) << endl;
      }
      else {
        cout << n - (evenMax[0].cnt + oddMax[1].cnt) << endl;
      }

    }
    else {
      cout << n - (evenMax[0].cnt + oddMax[0].cnt) << endl;
    }
  }

  return 0;

}