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)

#![allow(unused_imports)]

#[macro_use]
mod _input {
    use std::fmt;
    use std::io::{self, Read};
    use std::str::{self, FromStr};

    macro_rules! input {
        ($($name:ident : $t:tt), *,) => {
            input!($($name: $t),*)
        };
        ($($name:ident : $t:tt), *) => {
            let ($($name, )*) = {
                let mut _scanned = ::_input::Scanned::new(::std::io::stdin(), 1024);
                $(let $name = _read_value!(_scanned, $t);)*
                ($($name, )*)
            };
            $(let _ = &$name;)*
        };
    }

    macro_rules! _read_value {
        ($scanned:expr, ($($t:tt), *)) => {
            ($(_read_value!($scanned, $t)), *)
        };
        ($scanned:expr, [$t:tt; $n:expr]) => {
            (0..$n).map(|_| _read_value!($scanned, $t)).collect::<Vec<_>>()
        };
        ($scanned:expr, _bytes) => {
            _read_value!($scanned, String).into_bytes()
        };
        ($scanned:expr, _index) => {
            _read_value!($scanned, usize) - 1
        };
        ($scanned:expr, $t:ty) => {
            $scanned.next::<$t>()
        };
    }

    #[derive(Default)]
    pub struct Scanned {
        buf: Vec<u8>,
        pos: usize,
    }

    impl Scanned {
        pub fn new<R: Read>(mut input: R, estimated: usize) -> Self {
            let mut buf = Vec::with_capacity(estimated);
            let _ = io::copy(&mut input, &mut buf).unwrap();
            // if buf.last() != Some(&b'\n') {
            //     buf.push(b'\n');
            // }
            // assert!(buf.iter().all(|&b| b <= 0x7f));
            Scanned { buf: buf, pos: 0 }
        }

        #[inline]
        pub fn next<T: FromStr>(&mut self) -> T
        where
            T::Err: fmt::Debug,
        {
            let mut start = None;
            loop {
                match (self.buf[self.pos], start.is_some()) {
                    (b' ', true) | (b'\n', true) => break,
                    (_, true) | (b' ', false) | (b'\n', false) => self.pos += 1,
                    (_, false) => start = Some(self.pos),
                }
            }
            let target = &self.buf[start.unwrap()..self.pos];
            unsafe { str::from_utf8_unchecked(target) }.parse().unwrap()
        }
    }
}

#[allow(dead_code)]
mod output {
    use std::io::{self, BufWriter, StdoutLock, Write as _Write};

    pub fn with_stdout<F: FnMut(&mut BufWriter<StdoutLock>)>(mut f: F) {
        let stdout = io::stdout();
        let mut stdout = BufWriter::new(stdout.lock());
        f(&mut stdout);
        stdout.flush().unwrap();
    }
}

use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
use std::io::Write;
use std::ops::{
    Add, AddAssign, BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Div, DivAssign,
    Mul, MulAssign, Neg, Not, Rem, RemAssign, Sub, SubAssign,
};
use std::str::{self, FromStr};
use std::{char, cmp, f32, f64, fmt, i16, i32, i64, i8, thread, u16, u32, u64, u8};

fn main() {
    input!{
        n: usize,
        vs: [u32; n],
    }
    let (mut es, mut os) = (BTreeMap::new(), BTreeMap::new());
    for (i, &v) in vs.iter().enumerate() {
        *(if i % 2 == 0 {
            es.entry(v).or_insert(0)
        } else {
            os.entry(v).or_insert(0)
        }) += 1;
    }
    let mut es = es.into_iter().collect::<Vec<_>>();
    let mut os = os.into_iter().collect::<Vec<_>>();
    es.sort_by_key(|p| p.1);
    os.sort_by_key(|p| p.1);
    let r = if es.last().unwrap().0 == os.last().unwrap().0 {
        let e_last = es.last().unwrap().1;
        let e_last_ = es.iter().rev().nth(1).map(|p| p.1).unwrap_or(0);
        let o_last = os.last().unwrap().1;
        let o_last_ = os.iter().rev().nth(1).map(|p| p.1).unwrap_or(0);
        let r1 = n - e_last - o_last_;
        let r2 = n - e_last_ - o_last;
        cmp::min(r1, r2)
    } else {
        n - es.last().unwrap().1 - os.last().unwrap().1
    };
    println!("{}", r);
}