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: Wrong Answer)

use std::collections::HashMap;

fn read_usize() -> usize {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    input.trim().parse().unwrap()
}

fn read_usizevec() -> Vec<usize> {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    input.trim().split_whitespace().map(|x| x.parse().unwrap()).collect()
}

fn map_update(map: &mut HashMap<usize, usize>, item: &usize) -> () {
    if map.contains_key(item) {
        if let Some(x) = map.get_mut(item) {
            *x += 1;
        }
    } else {
        map.insert(*item, 1usize);
    }
}

fn count_1st_2nd(map: &HashMap<usize, usize>) -> (usize, usize) {
    let (mut num_1st, mut num_2nd) = (0, 0);
    for value in map.values() {
        if value >= &num_1st {
            num_2nd = num_1st;
            num_1st = *value;
        }
    }
    (num_1st, num_2nd)
}

fn main() {
    let n = read_usize();
    let v = read_usizevec();
    let mut map_evens: HashMap<usize, usize> = HashMap::new();
    let mut map_odds: HashMap<usize, usize> = HashMap::new();
    for (i, item) in v.iter().enumerate() {
        if i % 2 == 0 {
            map_update(&mut map_evens, item);
        } else {
            map_update(&mut map_odds, item);
        }
    }

    let (even_1st, even_2nd) = count_1st_2nd(&map_evens);
    let (odd_1st, odd_2nd) = count_1st_2nd(&map_odds);

    if even_1st + odd_2nd < even_2nd + odd_1st {
        println!("{}", even_1st + odd_1st);
    } else {
        if map_evens.eq(&map_odds) {
            println!("{}", n / 2);
        } else {
            println!("{}", even_2nd + odd_2nd);
        }
    }
}