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 (2.7.6) (judge verdict: Accepted)

#!/bin/env python

def count_nums(v):
    counter = {}
    for x in v:
        if x not in counter:
            counter[x] = 0
        counter[x] += 1
    retval = counter.items()
    retval.sort(lambda a,b:b[1] - a[1])
    # i : index
    # retval[i][0] : number
    # retval[i][1] : count
    # retval is sorted by count
    return retval

def main():
    n = int(raw_input().strip())
    v = raw_input().strip().split(" ")
    v1 = [int(v[x]) for x in xrange(0, n, 2)]
    v2 = [int(v[x]) for x in xrange(1, n, 2)]

    cv1 = count_nums(v1)
    cv2 = count_nums(v2)

    if cv1[0][0] != cv2[0][0]:
        print n - (cv1[0][1] + cv2[0][1])
    elif len(cv1) == 1 and len(cv2) == 1:
        print len(v2)
    elif len(cv1) == 1:
        print len(v2) - cv2[1][1]
    elif len(cv2) == 1:
        print len(v1) - cv1[1][1]
    else:
        print n - max(cv1[0][1]+cv2[1][1], cv1[1][1]+cv2[0][1])

if __name__ == '__main__':
    main()