Manacher模板

#include <cstdio>
#include <cmath>
#include <deque>
#include <stack>
#include <queue>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
#define ll long long
#define ull unsigned long long

const int Maxn=22000001;
const int inf=2147483647;

int n,m,hw[Maxn];
char s[Maxn],a[Maxn];
void change() {
    s[0]=s[1]=‘#‘;
    for(int i=0; i<n; i++) {
        s[i*2+2]=a[i];
        s[i*2+3]=‘#‘;
    }
    n=n*2+2;
    s[n]=0;
    return;
}
int main() {
    cin>>a;
    n=strlen(a);
    change();
    int r=0,mid=0;
    for(int i=1; i<n; i++) {
        if(i<r) hw[i]=min(hw[mid-(i-mid)],hw[mid]-(i-mid));
        else hw[i]=1;
        while(s[i+hw[i]]==s[i-hw[i]]) ++hw[i];
        if(i+hw[i]>r) {
            r=hw[i]+i;
            mid=i;
        }
    }
    int ans=1;
    for(int i=0; i<n; i++)    ans=max(ans,hw[i]);
    cout<<ans-1<<endl;
    return 0;
}