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 <unordered_map>
#include <algorithm>
using namespace std;

int max_frequency(vector<int> vint) {
  unordered_map<int, int> hash;
  for (auto i = 0; i < vint.size(); i++) {
    hash[vint[i]]++;
  }
  int max_count = 0;
  for (auto i : hash) {
    if (max_count <= i.second)
      max_count = i.second;
  }
  return max_count;
}

int main(int argc, char *argv[]) {
  int n;
  vector<int> vint;
  bool all_the_same = true;

  cin >> n;
  for (auto i = 0; i < n; i++) {
    int temp;
    cin >> temp;
    vint.emplace_back(temp);
  }

  vector<int> vfirst;
  vector<int> vsecond;
  vector<int> vclone = vint;
  sort(vclone.begin(), vclone.end());
  if (vclone[0] != vclone[n-1]) all_the_same = false;

  if (all_the_same) {
    cout << n / 2;
  } else {
    for (auto i = 0; i < n/2; i++) {
      vfirst.emplace_back(vint[2*i]);
      vsecond.emplace_back(vint[2*i+1]);
    }
    int count = n - max_frequency(vfirst) - max_frequency(vsecond);
    cout << count;
  }

  return 0;
}