代码

#include<cstdio>
#include<algorithm>
using namespace std;
int T,n,a[23],b[23];
bool check(){
	int tot=0,ans=0;
	for (int i=1;i<=n;i++) {
		b[i]=a[i];
		tot+=abs(i-b[i]);
	}
	for (int i=1;i<=n;i++)
		for (int j=1;j<n;j++)
			if (b[j]>b[j+1]) {
				swap(b[j],b[j+1]);
				ans++;
			}
	return ans*2==tot;
}
int main(){
	scanf("%d",&T);
	while (T--){
		scanf("%d",&n);
		if (n>20) return 0;
		for (int i=1;i<=n;i++) scanf("%d",a+i);
		int ans=0;
		while (next_permutation(a+1,a+n+1))
			if (check()) ans++;
		printf("%d\n",ans%998244353);
	}
	return 0;
}

评测结果