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: Wrong Answer)

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

using namespace std;

struct numAndCnt {
  int num;
  int cnt;
};

int main()
{
  /* Input */
  int n;
  cin >> n;

  vector<int> evenSeries(n / 2);  //偶数部
  vector<int> oddSeries(n / 2); //奇数部

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

    if (id % 2 == 0) {
      evenSeries[evenIdCnt] = val;
      evenIdCnt++;
    }
    else {
      oddSeries[oddIdCnt] = val;
      oddIdCnt++;
    }
  }

  sort(evenSeries.begin(), evenSeries.end());
  sort(oddSeries.begin(), oddSeries.end());

  /* Create List of num and count. */ 
  evenIdCnt = 0;
  vector<numAndCnt> evenMax;
  numAndCnt tempEvenIns;
  tempEvenIns.num = evenSeries[0];
  tempEvenIns.cnt = count(evenSeries.begin(), evenSeries.end(), evenSeries[0]);
  evenMax.push_back(tempEvenIns);
  for (int id = 0; id < evenSeries.size(); id++) {
    tempEvenIns.num = evenSeries[id];
    if (evenMax[evenMax.size() - 1].num != tempEvenIns.num) {
      tempEvenIns.cnt = evenIdCnt;
      evenMax.push_back(tempEvenIns);
      evenIdCnt = 0;
    }
    evenIdCnt++;
  }
  oddIdCnt = 0;
  vector<numAndCnt> oddMax;
  numAndCnt tempOddIns;
  tempOddIns.num = oddSeries[0];
  tempOddIns.cnt = count(oddSeries.begin(), oddSeries.end(), oddSeries[0]);
  oddMax.push_back(tempOddIns);
  for (int id = 0; id < oddSeries.size(); id++) {
    tempOddIns.num = oddSeries[id];
    if (oddMax[oddMax.size() - 1].num != tempOddIns.num) {
      tempOddIns.cnt = oddIdCnt;
      oddMax.push_back(tempOddIns);
      oddIdCnt = 0;
    }
    oddIdCnt++;
  }

  /* 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; });

  if (evenMax[0].num == oddMax[0].num) {
    if (evenMax.size() == 1 && oddMax.size() == 1) {
      cout << n / 2 << endl;
    }
    else if (evenMax.size() == 1 && oddMax.size() > 1) {
      cout << n / 2 - oddMax[1].cnt << endl;
    }
    else if (evenMax.size() > 1 && oddMax.size() == 1) {
      cout << n / 2 - evenMax[1].cnt << endl;
    } 
    else {
      if (evenMax[1].cnt > oddMax[1].cnt) {
        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;
}