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;

#[allow(unused_macros)]
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)*}
    };
}

#[allow(unused_macros)]
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)*}
    };
}

#[allow(unused_macros)]
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>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

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

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

fn max_nums(v: &Vec<i64>) -> (Vec<(i64, i64)>, Vec<(i64, i64)>) {
    let mut sum_0: HashMap<i64, i64> = HashMap::new();
    let mut sum_1: HashMap<i64, i64> = HashMap::new();
    for i in 0..v.len() {
        let i = 0 + i * 2;
        if i >= v.len() {
            break;
        }
        let num = {
            if let Some(num) = sum_0.get(&v[i]) {
                *num + 1
            } else {
                1
            }
        };
        sum_0.insert(v[i], num);
    }
    for i in 1..v.len() {
        let i = 1 + (i - 1) * 2;
        if i >= v.len() {
            break;
        }
        let num = {
            if let Some(num) = sum_1.get(&v[i]) {
                *num + 1
            } else {
                1
            }
        };
        sum_1.insert(v[i], num);
    }
    let mut v0 = sum_0.into_iter().collect::<Vec<(i64, i64)>>();
    v0.sort_by(|a, b| b.1.cmp(&a.1));
    let mut v1 = sum_1.into_iter().collect::<Vec<(i64, i64)>>();
    v1.sort_by(|a, b| b.1.cmp(&a.1));
    (v0, v1)
}

fn flip(v: &Vec<i64>) -> i64 {
    let (v0, v1) = max_nums(v);
    if v0[0].0 == v1[0].0 {
        if v0.len() == 1 && v1.len() == 1 {
            return v.len() as i64 / 2;
        }
        if v0.len() == 1 {
            return v.len() as i64 / 2 - v1[1].1;
        }
        if v1.len() == 1 {
            return v.len() as i64 / 2 - v0[1].1;
        }
        return std::cmp::min(
            v.len() as i64 - v0[0].1 - v1[1].1,
            v.len() as i64 - v0[1].1 - v1[0].1,
        );
    }
    let result = v.len() as i64 - v0[0].1 - v1[0].1;
    result
}

fn main() {
    input! {
        n: i64,
        v: [i64; n],
    };
    let result = flip(&v);
    println!("{}", result);
}