bzoj4416: [Shoi2013]阶乘字符串

#include<cstdio>
void up(int& a,int b){
	a=a<b?b:a;
}
int test,n,m,i,j;
char t[500];
int f[1<<21],s[500][21];
int main(){
	scanf("%d",&test);
	while(test--){
		scanf("%d%s",&n,t);
		if(n>21)puts("NO");
		if(n>21)continue;
		for(m=0;t[m];++m)
			t[m]-=97;
		for(j=0;j<n;++j)
			s[m+1][j]=s[m][j]=m+1;
		for(i=m-1;~i;--i)
			for(j=0;j<n;++j)
				s[i][j]=j==t[i]
				?i+1:s[i+1][j];
		for(i=1;i<1<<n;++i)
			for(f[i]=j=0;j<n;++j)
				if(i&1<<j)up(f[i],
				s[f[i^1<<j]][j]);
		puts(f[~(~0<<n)]
		<=m?"YES":"NO");
	}
}