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::io;
use std::cmp;
use std::collections::BinaryHeap;
use std::collections::HashMap;

fn read_line() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).ok();
    buf
}

fn main() {
    let n:usize = read_line().trim().parse().unwrap();
    let arr: Vec<usize> = read_line().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mut mp1 = HashMap::new();
    let mut mp2 = HashMap::new();

    for i in 0..n {
        let key = arr[i];
        if i%2 == 0 {
            let val = mp1.get(&key).unwrap_or(&0) + 1;
            mp1.insert(key, val);
        } else {
            let val = mp2.get(&key).unwrap_or(&0) + 1;
            mp2.insert(key, val);
        }
    }

    let mut vals1: Vec<(&usize,&usize)>= mp1.iter().collect();
    let mut vals2: Vec<(&usize,&usize)> = mp2.iter().collect();
    vals1.sort_by(|e1,e2| e2.1.cmp(&e1.1));
    vals2.sort_by(|e1,e2| e2.1.cmp(&e1.1));

    if (vals1[0].0 != vals2[0].0) {
        println!("{}", n - vals1[0].1 - vals2[0].1);
    } else {
        if vals1.len() == 1 && vals2.len() == 1 {
            println!("{}", n/2);
        } else if vals1.len() == 1 {
            println!("{}", n/2 - vals2[1].1);
        } else if vals2.len() == 1 {
            println!("{}", n/2 - vals1[1].1);
        } else {
            println!("{}", cmp::min(n - vals1[0].1 - vals2[1].1, n - vals1[1].1 - vals2[0].1));
        }
    }
}