下列程序以O(n)的复杂度完成了这个任务，请完善程序
#include <bits/stdc++.h>
using namespace std;
int main()
{
int N;
cin >> N;
vector<int> a(N, 0);
vector<int> count(3, 0);
for (int i = 0; i < N; i++)
{
cin >> a[i];
______(1)_________;
}
vector<vector<int> > map(3, vector<int>(3, 0));
for (int i = 0; i < N; i++)
{
if (i < count[0])
map[0][a[i] - 1]++;
else if (i < ______(2)_______)
map[1][a[i] - 1]++;
else
map[2][a[i] - 1]++;
}
int ans = 0;
int diff = ______(3)________;
ans += diff;
map[0][1] -= diff;
map[1][0] -= diff;
diff = min(map[0][2], map[2][0]);
ans += diff;
map[0][2] -= diff;
map[2][0] -= diff;
diff = min(map[1][2], map[2][1]);
ans += diff;
map[1][2] -= diff;
map[2][1] -= diff;
diff = _______(4)_______;
ans += _______(5)_______;
cout << ans << endl;
return 0;
}