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 <bits/stdc++.h>
using namespace std;

int main(){
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i=0; i<n; i++) cin >> v[i];
  vector<int>od(100001,0), ev(100001,0);
  for (int i=0; i<n; i++){
    if (i%2==0) ev[v[i]]++;
    else od[v[i]]++;
  }
  int evfir=0, evsec=0, odfir=0, odsec=0;
  int evfirind=-1,evsecind=-1,odfirind=-1,odsecind=-1;
  for (int i=0; i<100001; i++){
    if (od[i] > odfir){
      odsec = odfir;
      odfir = od[i];
      odsecind = odfirind;
      odfirind = i;
    }
    else if (od[i] > odsec){
      odsec = od[i];
      odsecind = i;
    }
    if (ev[i] > evfir){
      evsec = evfir;
      evfir = ev[i];
      evsecind = evfirind;
      evfirind = i;
    }
    else if (ev[i] > evsec) evsec = ev[i];
  }
  int ans;
  if (odfirind != evfirind) ans = n-odfir-evfir;
  else if ((odsecind==-1)||(evsecind==-1)) ans = n/2;
  else ans = min(n-odfir-evsec, n-odsec-evfir);
  cout << ans << endl;
}