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)

// 入力マクロ
// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

use std::collections::HashMap;

fn main() {
    input! {
        n: usize,
        a: [usize; n]
    }

    let mut e = count_map(
        &a.iter()
            .enumerate()
            .filter(|x| x.0 % 2 == 0)
            .map(|x| *x.1)
            .collect(),
    )
    .into_iter()
    .collect::<Vec<(usize, usize)>>();
    e.sort_by(|a, b| (b.1).cmp(&a.1));
    let mut o = count_map(
        &a.iter()
            .enumerate()
            .filter(|x| x.0 % 2 == 1)
            .map(|x| *x.1)
            .collect(),
    )
    .into_iter()
    .collect::<Vec<(usize, usize)>>();
    o.sort_by(|a, b| (b.1).cmp(&a.1));

    let ans = if e[0].0 != o[0].0 {
        n - e[0].1 - o[0].1
    } else {
        std::cmp::min(
            n - if e.len() == 1 { 0 } else { e[1].1 } - o[0].1,
            n - if o.len() == 1 { 0 } else { o[1].1 } - e[0].1,
        )
    };

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

fn count_map<T: Eq + std::hash::Hash + Copy>(v: &Vec<T>) -> std::collections::HashMap<T, usize> {
    let mut map = HashMap::new();
    for e in v {
        let h = map.entry(*e).or_insert(0);
        *h += 1;
    }
    map
}