P3805 【模板】manacher算法

 #include <bits/stdc++.h>
 #define up(i,l,r) for(register int i = (l);i <= (r); i++)
 #define dn(i,l,r) for(register int i = (l);i >= (r); i--)
 #define ll long long
 using namespace std;

 const int N = ;
 int len,ans,r[N<<];
 char s[N],str[N<<];

 void init(){
     len = strlen(s+);
     int k = -;
     str[++k] = '$';
     up(i,,len){
         str[++k] = '#';
         str[++k] = s[i];
     }
     str[++k] = '#';
     len = k;
 }

 void Manacher(){
     init();
     int id = ,mx = ;
     up(i,,len-){
         if(mx > i) r[i] = min(r[id*-i],mx-i);
         else r[i] = ;
         while(str[i+r[i]] == str[i-r[i]]) ++r[i];
         if(i+r[i] > mx){
             mx = i+r[i];
             id = i;
             ans = max(ans,r[i]);
         }
     }
     printf("%d",ans-);
 }

 int main(){
     scanf("%s",s+);
     Manacher();
     return ;
 }