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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(void) {
  int n;
  scanf("%d", &n);

  typedef struct {
    int vn;
    int num;
  } cnt;

  cnt c1[100000 / 2];
  cnt c2[100000 / 2];
  int c1_idx = 0;
  int c2_idx = 0;
  for(int i = 0; i < n; i++)  {
    int v;
    scanf("%d", &v);

    cnt *c;
    int *idx;
    if(i % 2 == 0) {
      c = c1;
      idx = &c1_idx;
    } else {
      c = c2;
      idx = &c2_idx;
    }

    int flag = 0;
    for(int j = 0; j < *idx; j++) {
      if(c[j].vn == v) {
	c[j].num++; 
	flag = 1;
	break;
      }
    }

    if(flag == 0){
      c[*idx].vn = v;
      c[*idx].num = 1;
      *idx = *idx + 1;
    }
  }

#ifdef DEBUG  
  for(int i = 0; i < c1_idx; i++) {
    printf("c1[%d].vn == %d, num == %d\n", i, c1[i].vn, c1[i].num);
  }
  for(int i = 0; i < c2_idx; i++) {
    printf("c2[%d].vn == %d, num == %d\n", i, c2[i].vn, c2[i].num);
  }
#endif

  // Search Maximum Number
  int c1_max1 = 0;
  int c1_max2 = 0;
  int c1_idx1;
  for(int i = 0; i < c1_idx; i++) {
    if(c1[i].num >= c1_max1) {
      c1_max2 = c1_max1;
      c1_max1 = c1[i].num;
      c1_idx1 = i;
    } else if(c1[i].num > c1_max2) {
      c1_max2 = c1[i].num;
    }
  }

  int c2_max1 = 0;
  int c2_max2 = 0;
  int c2_idx1;
  for(int i = 0; i < c2_idx; i++) {
    if(c2[i].num >= c2_max1) {
      c2_max2 = c2_max1;
      c2_max1 = c2[i].num;
      c2_idx1 = i;
    } else if(c2[i].num > c2_max2) {
      c2_max2 = c2[i].num;
    }
  }

  if(c1[c1_idx1].vn == c2[c2_idx1].vn) {// same number..
    if((c1_max1 + c2_max2) < (c2_max1 + c1_max2)) {// c1 will be modified.
      c2_max1 = c2_max2;
    } else {// c2 will be modified.
      c1_max1 = c1_max2;
    }
  }

  // c1 and c2 is different number
  printf("%d\n", n - (c1_max1 + c2_max1));

  return 0;
}