# [bzoj3160]万径人踪灭

## Solution

$x-a=b-x\\ \rightarrow a+b=2x$

## Code

/**************************************************************
Problem: 3160
User: PaperCloud
Language: C++
Result: Accepted
Time:7748 ms
Memory:15648 kb
****************************************************************/

#include<bits/stdc++.h>
#define min(a,b) ((a)<(b)?(a):(b))
#define max(a,b) ((a)>(b)?(a):(b))
#define reg register
#define ll long long
#define db double
#define int ll
#define PaperCloud FallDream
const int Mod=998244353,g=3,invg=332748118,P=1e9+7;
int Mul(int a,int b,int M=Mod){return (1ll*a*b)%M;}
int Add(int a,int b,int M=Mod){return (a+b)%M;}
int fpow(int a,int b,int M=Mod){int r=1;for(;b;b>>=1,a=Mul(a,a,M))if(b&1)r=Mul(r,a,M);return r;}
void NTT(int *a,int N,int ty,int *pos)
{
int w,wn,i,j,p,k,X,Y;
for(i=0;i<N;++i) if(pos[i]>i) std::swap(a[i],a[pos[i]]);
for(i=1;i<N;i<<=1)
{
w=fpow(ty>0?g:invg,(Mod-1)/(i<<1));
for(j=0,p=(i<<1);j<N;j+=p)
for(wn=1,k=0;k<i;++k,wn=Mul(wn,w))
{
X=a[j+k],Y=Mul(a[j+i+k],wn);
}
}
if(ty==-1)for(j=fpow(N,Mod-2),i=0;i<N;++i)a[i]=Mul(a[i],j);
}
const int MN=1e5+5;
char s[MN*3];
int a[2][MN*5],p[MN*3],ans,pos[MN*5];
int Calc(int len)
{
s[len*2+1]='$'; for(int i=len;i;--i) s[i*2]=s[i-1],s[i*2-1]='$';
s[0]='*';
int mx=0,id=0;
for(int i=1;i<=(len<<1);++i)
{
p[i]=mx>i?min(p[id*2-i],mx-i):1;
while(s[i+p[i]]==s[i-p[i]])++p[i];
if(i+p[i]>mx)id=i,mx=p[i]+i;
}
ll r=0;
return r;
}
signed main()
{
scanf("%s",s);
int len=strlen(s);
int N,i,j;
for(N=1;N<len*2;N<<=1);
memset(a,0,sizeof a);
for(i=0;i<len;++i) a[s[i]=='b'][i]=1;
for(i=0;i<N;++i) pos[i]=(pos[i>>1]>>1)|((i&1)*(N>>1));
//  for(i=0;i<len*2-1;++i) printf("%d : %d %d \n",i,a[0][i],a[1][i]);
for(i=0;i<2;++i)
{
NTT(a[i],N,1,pos);
for(j=0;j<N;++j) a[i][j]=Mul(a[i][j],a[i][j]);
NTT(a[i],N,-1,pos);
}