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 PyPy3 (2.4.0) (judge verdict: Accepted)

def run_length_compress(string):
    """文字列をランレングス圧縮する
    例) string = "aabccaaabb" -> [(2, a), (1, b), (2, c), (3, a), (2, b)]
    """
    string.append(-1) # string中に絶対に現れない文字を番兵とする
    n = len(string)

    begin = 0
    end = 1
    cnt = 1
    ans = []
    while True:
        if end >= n:
            break
        if string[begin] == string[end]:
            end += 1
            cnt += 1
        else:
            ans.append((cnt, string[begin]))
            begin = end
            end = begin + 1
            cnt = 1

    return ans
  
n = int(input())
v = list(map(int, input().split()))
even = []
odd = []

for i in range(n):
    if i % 2 == 0:
        even.append(v[i])
    else:
        odd.append(v[i])
memo_o = {}
for num in odd:
    if num not in memo_o:
        memo_o[num] = 1
    else:
        memo_o[num] += 1

even = sorted(even)
even = run_length_compress(even)
even = sorted(even, reverse = True)
ans = 10 ** 9
for i in memo_o:
    tmp = n // 2 - memo_o[i]
    tmp2 = n // 2
    for cnt, num in even[:2]:
        if i != num:
            tmp2 = min(n // 2 - cnt, tmp2)
    ans = min(ans, tmp + tmp2)
print(ans)