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::{self, BufRead};
use std::collections::HashMap;
use std::cmp::min;

fn main() {
  let stdin = io::stdin();
  let mut lines = stdin.lock().lines();
  let _: usize = lines.next().unwrap().unwrap().parse().unwrap();
  let vs: Vec<usize> = lines.next().unwrap().unwrap().split(' ').map(|x| x.parse().unwrap()).collect();
  let mut xs: HashMap<usize, usize> = HashMap::new();
  let mut ys: HashMap<usize, usize> = HashMap::new();
  for i in 0..vs.len() {
    let k = vs[i];
    if i % 2 == 0 {
      let v = xs.get(&k).unwrap_or(&0).clone();
      xs.insert(k, v + 1);
    } else {
      let v = ys.get(&k).unwrap_or(&0).clone();
      ys.insert(k, v + 1);
    }
  }
  let (kx, vx) = xs.iter().max_by(|x, y| x.1.cmp(y.1)).unwrap();
  let (ky, vy) = ys.iter().max_by(|x, y| x.1.cmp(y.1)).unwrap();
  let nx = (vs.len() + 1) / 2 - vx;
  let ny = vs.len() / 2 - vy;
  let ans = if kx != ky {
    nx + ny
  } else {
    let zero = 0;
    let (_, vx2) = xs.iter().filter(|k| *k.0 != *kx).max_by(|x, y| x.1.cmp(y.1)).unwrap_or((&zero, &zero));
    let (_, vy2) = ys.iter().filter(|k| *k.0 != *ky).max_by(|x, y| x.1.cmp(y.1)).unwrap_or((&zero, &zero));
    let nx2 = (vs.len() + 1) / 2 - vx2;
    let ny2 = vs.len() / 2 - vy2;
    min(nx + ny2, nx2 + ny)
  };
  println!("{}", ans);
}