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::io::Read;
use std::collections::HashMap;

fn main() {
    // inputs
    let mut stdin = io::stdin();
    let mut lines_str = String::new();
    let _ = stdin.read_to_string(&mut lines_str);
    let mut lines = lines_str.lines();
    let n :usize = lines.next().expect("").trim().parse().unwrap();
    let mut v :Vec<usize> = Vec::new();
    let mut line2iter = lines.next().expect("").split_whitespace();
    for _ in 0..n {
        v.push(line2iter.next().expect("").trim().parse().unwrap());
    }
    let v = v;

    if n == 2 {
        if v[0] == v[1] {
            println!("1");
            return;
        } else {
            println!("0");
            return;
        }
    }

    let mut vodd_vallist :HashMap<usize,usize> = HashMap::new();
    for j in 0..(n/2) {
        let count = vodd_vallist.entry(v[2*j]).or_insert(0);
        *count += 1;
    }
    let mut vodd :Vec<(usize,usize)> = vodd_vallist.iter().map(|(&x,&y)| (x,y) ).collect();
    vodd.sort_by(|&y,&w| (w.1).cmp(&y.1));


    let mut veven_vallist :HashMap<usize,usize> = HashMap::new();
    for j in 0..(n/2) {
        let count = veven_vallist.entry(v[2*j+1]).or_insert(0);
        *count += 1;
    }
    let mut veven :Vec<(usize,usize)> = veven_vallist.iter().map(|(&x,&y)| (x,y) ).collect();
    veven.sort_by(|&y,&w| (w.1).cmp(&y.1));

    let answer;
    if vodd[0].0 == veven[0].0 {
        if vodd.len() == 1 {
            if veven.len() == 1 {
                answer = n/2;
            } else {
                answer = n - vodd[0].1 - veven[1].1;
            }
        } else if veven.len() == 1 {
            answer = n - vodd[1].1 - veven[0].1;
        } else if vodd[1].1 > veven[1].1 {
            answer = n - vodd[1].1 - veven[0].1;
        } else {
            answer = n - vodd[0].1 - veven[1].1;
        }
    } else {
        answer = n - vodd[0].1 - veven[0].1;
    }

    println!("{}",answer);
}