1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
| #include<bits/stdc++.h>
#define int long long
#define ull unsigned long long
#define maxn 200005
#define put() putchar('\n')
#define Tp template<typename Ty>
#define Ts template<typename Ty,typename... Ar>
using namespace std;
void read(int &x){
int f=1;x=0;char c=getchar();
while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
while (c>='0'&&c<='9') {x=x*10+c-'0';c=getchar();}
x*=f;
}
namespace Debug{
Tp void _debug(char* f,Ty t){cerr<<f<<'='<<t<<endl;}
Ts void _debug(char* f,Ty x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
Tp ostream& operator<<(ostream& os,vector<Ty>& V){os<<"[";for(auto& vv:V) os<<vv<<",";os<<"]";return os;}
#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
#define fi first
#define se second
#define mk make_pair
const int mod=998244353;
int power(int x,int y=mod-2) {
int sum=1;
while (y) {
if (y&1) sum=sum*x%mod;
x=x*x%mod;y>>=1;
}
return sum;
}
int fa[maxn];
int a[maxn],t[maxn];
int s[maxn],n,l,r,tot,c[maxn],vis[maxn];
const int base=2e5;
int getfa(int x) {return x==fa[x]?x:fa[x]=getfa(fa[x]);}
signed main(void){
int i,nums=0,cnt=0;
read(n);
for (i=1;i<=n;i++) read(a[i]),t[a[i]]++,nums+=(t[a[i]]==1);
for (i=1;i<=n;i++) {
if (l==r) tot++,fa[tot]=tot;
c[i]=tot;
if (l>r&&s[r+1]==a[i]) vis[a[i]]=0,r++;
else if (vis[a[i]]) return printf("%lld",power(2,nums-1)),0;
else s[++l]=a[i],vis[a[i]]=1;
}
if (l!=r) return printf("%lld",power(2,nums-1)),0;
for (i=1;i<=n;i++) t[a[i]]=0;
for (i=1;i<=n;i++) {
int las=t[a[i]];
if (las&&getfa(c[las])!=getfa(c[i])) fa[getfa(c[las])]=getfa(c[i]);
t[a[i]]=i;
}
for (i=1;i<=tot;i++) cnt+=(i==getfa(i));
printf("%lld",(power(2,nums-1)-power(2,cnt-1)+mod)%mod);
return 0;
}
|