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::collections::HashMap;

/// Rustで競技プログラミングの入力をスッキリ記述するマクロ
///
/// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
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")
    };
}

fn main() {
    input!{
        n: usize,
        vpair: [(u64, u64); n/2],
    }

    let mut a_count: HashMap<u64, _> = HashMap::new();
    let mut b_count: HashMap<u64, _> = HashMap::new();
    for &(a, b) in &vpair {
        *a_count.entry(a).or_insert(0) += 1;
        *b_count.entry(b).or_insert(0) += 1;
    }

    let mut a_count: Vec<(&u64, &u64)> = a_count.iter().collect();
    let mut b_count: Vec<(&u64, &u64)> = b_count.iter().collect();

    a_count.sort_by(|&(_, a), &(_, b)| b.cmp(a));
    b_count.sort_by(|&(_, a), &(_, b)| b.cmp(a));

    let mut a_i = 0usize;
    let mut b_i = 0usize;
    if a_count[a_i].0 != b_count[b_i].0 {
        println!("{}",
                 (n as u64 /2 - *a_count[a_i].1)
                 + (n as u64 /2 - *b_count[b_i].1));
    } else {
        let mut buf_ans_a = None;
        let mut buf_ans_b = None;
        if a_i != a_count.len() - 1 {
            // a_i を動かす
            buf_ans_a = Some((n as u64 /2 - *a_count[a_i + 1].1)
                             + (n as u64 /2 - *b_count[b_i].1));
        }

        if b_i != b_count.len() - 1 {
            // b_i を動かす
            buf_ans_b = Some((n as u64 /2 - *a_count[a_i].1)
                             + (n as u64 /2 - *b_count[b_i + 1].1));
        }

        println!("{}",
                 match (buf_ans_a, buf_ans_b) {
                     (Some(buf_ans_a), Some(buf_ans_b)) => {
                         std::cmp::min(buf_ans_a, buf_ans_b)
                     }
                     (Some(buf_ans_a), None) => { buf_ans_a }
                     (None, Some(buf_ans_b)) => { buf_ans_b }
                     (None, None) => { n as u64 / 2 }
                 }
        );
    }
}