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! get {
    ([$t:ty] ; $n:expr) => {
        (0..$n)
        .map(|_| get!([$t])).collect::<Vec<_>>()
    };
    ($($t:ty),+ ; $n:expr) => {
        (0..$n).map(|_| get!($($t),+)).collect::<Vec<_>>()
    };
    ([$t:ty]) => {
        rl().split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect::<Vec<$t>>()
    };
    ($t:ty) => {
        rl().parse::<$t>().unwrap()
    };
    ($($t:ty),*) => {
        {
            let line =rl();
            let mut iter = line.split_whitespace();
            ($(iter.next().unwrap().parse::<$t>().unwrap()),*)
        }
    };
}
fn rl() -> String {
    let mut line = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    line.trim().to_string()
}

fn main() {
    let n = get!(usize);
    let v = get!([usize]);
    let mut even = HashMap::with_capacity(n / 2);
    let mut odd = HashMap::with_capacity(n / 2);
    for (i, x) in v.iter().enumerate() {
        if i % 2 == 0 {
            let counter = even.entry(x).or_insert(0);
            *counter += 1;
        } else {
            let counter = odd.entry(x).or_insert(0);
            *counter += 1;
        }
    }
    let mut e_max_val = 0;
    let mut e_second_val = 0;
    let mut key_of_e_max_val = 0;
    for (key, val) in even.iter() {
        if e_max_val <= *val {
            key_of_e_max_val = **key;
            e_second_val = e_max_val;
            e_max_val = *val;
        } else if e_second_val <= *val {
            e_second_val = *val;
        }
    }
    let mut o_max_val = 0;
    let mut o_second_val = 0;
    let mut key_of_o_max_val = 0;
    for (key, val) in odd.iter() {
        if o_max_val <= *val {
            key_of_o_max_val = **key;
            o_second_val = o_max_val;
            o_max_val = *val;
        } else if o_second_val <= *val {
            o_second_val = *val;
        }
    }
    //eprintln!(
    //    "key_of_e_max_val: {}, e_max_val: {}, e_second_val: {}",
    //    key_of_e_max_val, e_max_val, e_second_val
    //);
    //eprintln!(
    //    "key_of_o_max_val: {}, o_max_val: {}, o_second_val: {}",
    //    key_of_o_max_val, o_max_val, o_second_val
    //);
    if key_of_e_max_val != key_of_o_max_val {
        println!("{}", n - e_max_val - o_max_val);
    } else {
        println!(
            "{}",
            std::cmp::min(n - e_max_val - o_second_val, n - e_second_val - o_max_val)
        );
    }
}