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 #include #include #include #include #include #include #define Fi first #define Se second #define ll_inf 1e18 #define MK make_pair #define sqr(x) ((x)*(x)) #define pii pair #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++; } templateinline 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; } templateinline 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; }