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 Python (3.4.3) (judge verdict: Accepted)

from collections import Counter

N = int(input())
V = tuple(map(int, input().split()))
X, Y = Counter(), Counter()
for i in range(0, N):
    if i & 1:
        Y[V[i]] += 1
    else:
        X[V[i]] += 1
if len(X) != 1:
    x = sorted(X.items(), reverse=True, key=lambda x: x[1])[:2]
else:
    x = sorted(X.items(), reverse=True, key=lambda x: x[1])[:1]
if len(Y) != 1:
    y = sorted(Y.items(), reverse=True, key=lambda x: x[1])[:2]
else:
    y = sorted(Y.items(), reverse=True, key=lambda x: x[1])[:1]
if x[0][0] == y[0][0]:
    ans = N
    tmp = 0
    if len(y) == 1:
        for i in range(0, N):
            if i & 1:
                if V[i] != y[0][0]+1:
                    tmp += 1
            else:
                if V[i] != x[0][0]:
                    tmp += 1
    else:
        for i in range(0, N):
            if i & 1:
                if V[i] != y[1][0]:
                    tmp += 1
            else:
                if V[i] != x[0][0]:
                    tmp += 1
    ans = min(ans, tmp)
    tmp = 0
    if len(x) == 1:
        for i in range(0, N):
            if i & 1:
                if V[i] != y[0][0]:
                    tmp += 1
            else:
                if V[i] != x[0][0]+1:
                    tmp += 1
    else:
        for i in range(0, N):
            if i & 1:
                if V[i] != y[0][0]:
                    tmp += 1
            else:
                if V[i] != x[1][0]:
                    tmp += 1
    ans = min(ans, tmp)
else:
    ans = 0
    for i in range(0, N):
        if i & 1:
            if V[i] != y[0][0]:
                ans += 1
        else:
            if V[i] != x[0][0]:
                ans += 1
print(ans)