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;

#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

fn max_nums(v: &Vec<i64>) -> (i64, i64) {
    let mut sum_0 = HashMap::new();
    let mut sum_1 = HashMap::new();
    for i in 0..v.len() {
        let i = 0 + i * 2;
        if i >= v.len() {
            break;
        }
        let contain = sum_0.get(&v[i]).is_some();
        if contain {
            let mut num = 0;
            {
                num = *sum_0.get(&v[i]).unwrap();
            }
            sum_0.insert(v[i], num + 1);
        } else {
            sum_0.insert(v[i], 1);
        }
    }
    for i in 1..v.len() {
        let i = 1 + i * 2;
        if i >= v.len() {
            break;
        }
        let contain = sum_1.get(&v[i]).is_some();
        if contain {
            let mut num = 0;
            {
                num = *sum_1.get(&v[i]).unwrap();
            }
            sum_1.insert(v[i], num + 1);
        } else {
            sum_1.insert(v[i], 1);
        }
    }

    let mut max_0_key = 0;
    let mut max_0_val = 0;
    let mut max_1_key = 0;
    let mut max_1_val = 0;
    for (key, val) in sum_0.iter() {
        if max_0_val < *val {
            max_0_key = *key;
            max_0_val = *val;
        }
    }
    for (key, val) in sum_1.iter() {
        if max_1_val < *val {
            max_1_key = *key;
            max_1_val = *val;
        }
    }
    (max_0_key, max_1_key)
}

fn flip(v: &Vec<i64>) -> i64 {
    let (n0, n1) = max_nums(v);
    if n0 == n1 {
        return (v.len() / 2) as i64;
    }
    let mut result = 0;
    for i in 0..v.len() {
        let i = 0 + i * 2;
        if i >= v.len() {
            break;
        }
        if v[i] != n0 {
            result += 1;
        }
    }
    for i in 1..v.len() {
        let i = 1 + i * 2;
        if i >= v.len() {
            break;
        }
        if v[i] != n1 {
            result += 1;
        }
    }
    result
}

fn main() {
    input! {
        n: i64,
        v: [i64; n],
    };
    let result = flip(&v);
    println!("{}", result);
}