CodeForces 1150C Prefix Sum Primes

解题思路
题目说给你一个个只有1和2的序列让你重新排列顺序，使前缀和具有更多的素数，每一个素数都是奇数，所以我们的排列过后应该不能放过任何一个奇数的组合可能，

#include <iostream>

using namespace std;

const int MAXN = 1e5 + 5;

int num;

int main()
{
	int n;
	cin >> n;
	int o = 0, t = 0;
	for (int i = 0; i < n; ++i)
	{
		cin >> num;
		if (num == 1)
		{
			o++;
		}
		else
		{
			t++;
		}
	}
	if (t == 0)
	{
		cout << 1;
		for (int i = 1; i < n; ++i)
		{
			cout << " " << 1;
		}
		cout << endl;
		return 0;
	}
	cout << 2 ;
	t--;
	if (o)
	{
		cout << " " << 1;
		o--;
	}
	for (int i = 0; i < t; ++i)
	{
		cout << " " << 2;
	}
	for (int i = 0; i < o; ++i)
	{
		cout << " " << 1;
	}
	cout << endl;
	return 0;
}