Submission #1690149

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Source Code Expand

#include<bits/stdc++.h>
#define ll long long
#define mod 1000000007
#define N 100009
using namespace std;

int n,a[N],fst[N],nxt[N],dgr[N],vis[N],num[N],f[N];
int main(){
	scanf("%d",&n);
	int i,j,k,sz,tmp,rst;
	for (i=1; i<=n; i++){
		scanf("%d",&a[i]);
		nxt[i]=fst[a[i]]; fst[a[i]]=i; dgr[a[i]]++;
	}
	int ans=1; bool flag;
	for (i=1; i<=n; i++) if (!vis[i]){
		for (j=i; !vis[j]; j=a[j]) vis[j]=1;
		sz=0; flag=1;
		for (; vis[j]!=2; j=a[j]){
			sz++; vis[j]=2;
			if (dgr[j]>2){ puts("0"); return 0; }
			else if (dgr[j]>1) flag=0;
		}
		if (flag){
			num[sz]++; continue;
		}
		for (; dgr[j]==1; j=a[j]); j=a[j];
		for (rst=0; vis[j]!=3; j=a[j]){
			vis[j]=3; rst++;
			for (k=fst[j]; k; k=nxt[k]) if (vis[k]<2){
				for (tmp=1; dgr[k]==1; k=fst[k]){
					vis[k]=1; tmp++;
				}
				vis[k]=1;
				if (dgr[k] || tmp>rst){ puts("0"); return 0; }
				if (rst>tmp) ans=(ans<<1)%mod;
				rst=0;
			}
		}
	}
	for (i=1; i<=n; i++){
		k=i>1 && (i&1)?2:1;
		for (j=f[0]=1; j<=num[i]; j++){
			f[j]=f[j-1]*k%mod;
			if (j>1) f[j]=(f[j]+(ll)f[j-2]*(j-1)%mod*i)%mod;
		}
		ans=(ll)ans*f[num[i]]%mod;
	} 
	printf("%d\n",ans);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:9:16: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
                ^
./Main.cpp:12:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);
                    ^

Judge Result