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;
use std::io::*;
use std::str::FromStr;

#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let n = read::<usize>();
    let mut seq = vec![0; n];
    let mut cnts = vec![HashMap::<usize, usize>::new(); 2];
    for i in 0..n {
        seq[i] = read::<usize>();
        let mut entry = cnts[i % 2].entry(seq[i]).or_insert(0);
        *entry += 1;
    }
    let mut ans = 0;
    let mut cnts2 = vec![vec![]; n];
    for i in 0..2 {
        for (&v, &cnt) in cnts[i].iter() {
            cnts2[i].push((cnt, v));
            ans = std::cmp::max(ans, cnt);
        }
        cnts2[i].sort();
        cnts2[i].reverse();
    }
    for i in 0..std::cmp::min(4, cnts2[0].len()) {
        for j in 0..std::cmp::min(4, cnts2[1].len()) {
            if cnts2[0][i].1 == cnts2[1][j].1 {
                continue;
            }
            ans = std::cmp::max(ans, cnts2[0][i].0 + cnts2[1][j].0);
        }
    }
    println!("{}", n - ans);
}