CF1149 A. Prefix Sum Primes

题目传送门：https://codeforces.com/problemset/problem/1149/A

题目大意：
给定一串长度为\(n\)的序列\(A\)，序列\(A\)仅由\(1,2\)组成，记\(S_i=\sum\limits_{j=1}^iA_j\)，问给序列\(A\)任意排序后，\(S\)中素数最多的情况？

---

由于素数除2之外都是偶数，故我们只需要构造形如\(2,1,2,...,2,1,...,1\)的序列即可

/*program from Wolfycz*/
#include<map>
#include<cmath>
#include<cstdio>
#include<vector>
#include<cstring>
#include<iostream>
#include<algorithm>
#define Fi first
#define Se second
#define ll_inf 1e18
#define MK make_pair
#define sqr(x) ((x)*(x))
#define pii pair<int,int>
#define int_inf 0x7f7f7f7f
using namespace std;
typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
inline char gc(){
	static char buf[1000000],*p1=buf,*p2=buf;
	return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
template<typename T>inline T frd(T x){
	int f=1; char ch=gc();
	for (;ch<'0'||ch>'9';ch=gc())	if (ch=='-')    f=-1;
	for (;ch>='0'&&ch<='9';ch=gc())	x=(x<<1)+(x<<3)+ch-'0';
	return x*f;
}
template<typename T>inline T read(T x){
	int f=1; char ch=getchar();
	for (;ch<'0'||ch>'9';ch=getchar())	if (ch=='-')	f=-1;
	for (;ch>='0'&&ch<='9';ch=getchar())	x=(x<<1)+(x<<3)+ch-'0';
	return x*f;
}
inline void print(int x){
	if (x<0)	putchar('-'),x=-x;
	if (x>9)	print(x/10);
	putchar(x%10+'0');
}
int Cnt[5];
int main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	int n=read(0);
	for (int i=1;i<=n;i++)	Cnt[read(0)]++;
	if (Cnt[2])	printf("2 "),Cnt[2]--;
	if (Cnt[1])	printf("1 "),Cnt[1]--;
	while (Cnt[2]--)	printf("2 ");
	while (Cnt[1]--)	printf("1 ");
	return 0;
}