manacher算法

模板题：洛谷p3805

code:

#include<iostream>
#include<algorithm>
using namespace std;
const int N=2.2e7+10;
string t,s;
int m,n;
int d[N];
int main(){
    cin>>t;
    m=t.size();
    s+=' ';
    for(auto ch: t){
        s+='#';
        s+=ch;
    }
    s+="##";
    n=s.size()-2;
    d[1]=1;
    int ret=1;
    for(int i=2,l=1,r=1;i<=n;i++){
        int len=r>=i?min(d[r-i+l],r-i+1):1;
        while(s[i+len]==s[i-len])
            len++;
        if(i+len-1>r){
            r=i+len-1;
            l=i-len+1;
        }
        d[i]=len;
        ret=max(ret,d[i]-1);
    }
    cout<<ret<<endl;
    return 0;
}