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<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}
fn main(){
    let n:i64 = read();
    let len = n /2;
    let an = read_vec::<i64>();
    if an.iter().all(|&x| x==an[0]){
        println!("{}",len);
        return;
    }
    let even:Vec<_> = an.iter().enumerate().filter(|&(i,v)| i % 2 == 0).map(|(k,v)|v).collect();
    let odd:Vec<_> =  an.iter().enumerate().filter(|&(i,v)| i % 2 != 0).map(|(k,v)|v).collect();
    let mut even_map:Vec<(_,_)> = even.iter().fold(HashMap::new(), |mut map, x| {
            let y = map.get(&x).map(|i| i + 1).unwrap_or(1);
            map.insert(x, y);
            map
        }).into_iter()
        .collect();
    even_map.sort();
    let mut odd_map:Vec<(_,_)> = odd.iter().fold(HashMap::new(), |mut map, x| {
            let y = map.get(&x).map(|i| i + 1).unwrap_or(1);
            map.insert(x, y);
            map
        }).into_iter()
        .collect();
    odd_map.sort();
    let even_diff = len - even_map.last().unwrap().1;
    let odd_diff = len -odd_map.last().unwrap().1;
    println!("{}",even_diff+odd_diff);
}