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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::*;
use std::str::FromStr;
use std::collections::HashMap;
use std::collections::BTreeSet;
use std::collections::HashSet;
use std::cmp;
use std::f64::consts;

fn main() {
    let n: i32 = read();
    let vec: Vec<i32> = (0..n).map(|_| read()).collect();
    let mut odd: HashMap<i32, i32> = HashMap::new();
    let mut even: HashMap<i32, i32> = HashMap::new();

    for (e, &i) in vec.iter().enumerate() {
        if e % 2 == 0 {
            if odd.contains_key(&i) {
                let v = odd.get(&i).unwrap().clone();
                odd.insert(i, v + 1);
            } else {
                odd.insert(i, 1);
            }
        } else {
            if even.contains_key(&i) {
                let v = even.get(&i).unwrap().clone();
                even.insert(i, v + 1);
            } else {
                even.insert(i, 1);
            }
        }
    }

    let mut saihin_odd: i32 = 0;
    let mut saihin_odd_key: i32 = 0;
    let mut saihin_even: i32 = 0;
    let mut saihin_even_key: i32 = 0;
    let mut next_odd: i32 = 0;
    let mut next_odd_key: i32 = 0;
    let mut next_even: i32 = 0;
    let mut next_even_key: i32 = 0;

    for (&key, &value) in odd.iter() {
        if value > saihin_odd {
            saihin_odd = value.clone();
            saihin_odd_key = key;
        }
    }

    for (&key, &value) in odd.iter() {
        if key != saihin_odd_key && value > next_odd {
            next_odd = value.clone();
            next_odd_key = key;
        }
    }

    for (&key, &value) in even.iter() {
        if value > saihin_even {
            saihin_even = value.clone();
            saihin_even_key = key;
        }
    }

    for (&key, &value) in even.iter() {
        if key != saihin_even_key && value > next_even {
            next_even = value.clone();
            next_even_key = key;
        }
    }

    let mut ans = (n/2) as i32 - saihin_odd + (n/2) as i32 - saihin_even;

    let set: HashSet<i32> = vec.into_iter().collect();

    if ans == 0 && set.len() == 1 {
        ans = (n/2);
    } else if saihin_odd_key == saihin_even_key {
        let a = (n/2) as i32 - saihin_odd + (n/2) as i32 - next_even;
        let b = (n/2) as i32 - next_odd + (n/2) as i32 - saihin_even;
        ans = cmp::min(a, b);
    }

    println!("{}", ans);
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}