题目连接

题面:

代码:

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#define ll long long
using namespace std;
const int maxn=22000100;
char str1[maxn];
char str2[maxn];
int p[maxn];

int Manacher(void)
{
    int k=0;
    str2[k++]='!';
    int len=strlen(str1);
    for(int i=0;i<len;i++)
        str2[k++]='#',str2[k++]=str1[i];
    str2[k++]='#';
    str2[k]=0;

    int sum=0;
    p[0]=1;
    int id=0,mx=0;
    int mid=0;

    for(int i=1;i<k;i++)
    {
        if(i<mx) p[i]=min(mx-i,p[2*id-i]);
        else p[i]=1;

        while(str2[i-p[i]]==str2[i+p[i]]) p[i]++;

        if(i+p[i]>mx)
        {
            mx=i+p[i];
            id=i;
        }

        sum=max(sum,p[i]);
    }
    return sum-1;
}

int main(void)
{
    scanf("%s",str1);
    printf("%d\n",Manacher());
    return 0;
}