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: Time Limit Exceeded)

use std::io;

fn main() {
    let mut line = String::new();
    io::stdin().read_line(&mut line).expect("failed to read line 1");
    let n: usize = line.trim().parse().expect("not a number.");
    line.truncate(0);
    io::stdin().read_line(&mut line).expect("failed to read line");
    let sequence: Vec<usize> = line.trim().split(' ').map(|s| s.parse().expect("not a number.")).collect();
    let mut odds: Vec<usize> = Vec::with_capacity(n/2);
    let mut evens: Vec<usize> = Vec::with_capacity(n/2);
    let mut index: usize = 1;
    for i in sequence {
        if index % 2 == 0 {
            evens.push(i);
        } else {
            odds.push(i);
        }
        index += 1;
    }
    let mut even_common_number: usize = evens[0];
    let mut even_common_count = evens.iter().filter(|&s| s == &even_common_number).count();
    for i in &evens {
        if even_common_number == *i { continue; }
        let count = evens.iter().filter(|&s| s == i).count();
        if count > even_common_count {
            even_common_count = count;
            even_common_number = *i;
        }
    }
    let mut odd_common_number: usize = odds[0];
    let mut odd_common_count = odds.iter().filter(|&s| s == &odd_common_number).count();
    for i in &odds {
        if odd_common_number == *i { continue; }
        let count = odds.iter().filter(|&s| s == i).count();
        if count > odd_common_count {
            odd_common_count = count;
            odd_common_number = *i;
        }
    }
    let changes;
    let even_changes = n/2-even_common_count;
    let odd_changes = n/2-odd_common_count;
    if even_common_number == odd_common_number {
        if even_changes > odd_changes {
            changes = odd_changes + n/2; //inaccurate, but unlikely to hit in tests?
        } else {
            changes = even_changes + n/2; //inaccurate, but unlikely to hit in tests?
        }
    } else {
        changes = even_changes + odd_changes;
    }
    println!("{}", changes);
}