BZOJ 2084: [Poi2010]Antisymmetry

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=5e5+5;
char s[N<<1]; int r[N<<1];
inline bool ok(char c1,char c2){
if(c1=='#' && c2=='#')return 1;
if(min(c1,c2)=='0' && max(c1,c2)=='1')return 1;
return 0;
}
int main(){
int n,id,mx=0,i,l=0;
scanf("%d",&n);
s[l]='^';
for(i=1;i<=n;++i){
s[++l]='#';
s[++l]=getchar();
while(s[l]<'0'||s[l]>'1')s[l]=getchar();
}
s[++l]='#',s[l+1]='*';
for(i=1;i<=l;++i){
if(mx>i)r[i]=min(r[2*id-i],mx-i);
while(ok(s[i-r[i]],s[i+r[i]]))
++r[i];
if(i+r[i]>mx) mx=i+r[i],id=i;
}
LL ans=0;
for(i=1;i<=l;++i)if(s[i]=='#')ans+=r[i]>>1;
printf("%lld\n",ans);
return 0;
}