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>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
using ll = int64_t;

int main() {
    int n;
    cin >> n;
    vector<int> odd;
    vector<int> even;
    rep(i, n) {
        int v;
        cin >> v;
        if (i % 2 == 0)
            even.push_back(v);
        else
            odd.push_back(v);
    }

    vector<int> oddNum(100001, 0);
    vector<int> evenNum(100001, 0);
    rep(i, n/ 2) {
        oddNum[odd[i]]++;
        evenNum[even[i]] += 1;
    }

    vector<int>::iterator oddMax1Itr = max_element(oddNum.begin(), oddNum.end());
    size_t oddMax1Idx = distance(oddNum.begin(), oddMax1Itr);
    int tmp = oddNum[oddMax1Idx];
    oddNum[oddMax1Idx] = -1;
    vector<int>::iterator oddMax2Itr = max_element(oddNum.begin(), oddNum.end());
    size_t oddMax2Idx = distance(oddNum.begin(), oddMax2Itr);
    oddNum[oddMax1Idx] = tmp;

    vector<int>::iterator evenMax1Itr = max_element(evenNum.begin(), evenNum.end());
    size_t evenMax1Idx = distance(evenNum.begin(), evenMax1Itr);
    tmp = evenNum[evenMax1Idx];
    evenNum[evenMax1Idx] = -1;
    vector<int>::iterator evenMax2Itr = max_element(evenNum.begin(), evenNum.end());
    size_t evenMax2Idx = distance(evenNum.begin(), evenMax2Itr);
    evenNum[evenMax1Idx] = tmp;

    ll ans = 0LL;
    if (oddMax1Idx != evenMax1Idx)
    {
        ans = n - oddNum[oddMax1Idx] - evenNum[evenMax1Idx];
    } else {
        if (oddNum[oddMax2Idx] > evenNum[oddMax2Idx]) {
            ans = n - oddNum[oddMax2Idx] - evenNum[evenMax1Idx];
        } else {
            ans = n - oddNum[oddMax1Idx] - evenNum[oddMax2Idx];
        }
    }

    cout << ans << endl;
}