马拉车算法

截图来自董老师https://www.bilibili.com/video/BV173411V7Ai/?spm_id_from=333.999.0.0&vd_source=23dc8e19d485a6ac47f03f6520fb15c2

  P3805 【模板】manacher 算法

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<stack>
#include<cstdio>
#include<queue>
#include<map>
#include<vector>
#include<set>
using namespace std;
const int maxn=3e7+10;
const int INF=0x3fffffff;
typedef long long LL;

char a[maxn],s[maxn];
int d[maxn];
void get_d(char *s,int n){
	d[1]=1;
	for(int i=2,l,r=1;i<=n;i++){
		if(i<=r) d[i]=min(d[r-i+l],r-i+1);
		while(s[i-d[i]]==s[i+d[i]]) d[i]++;
		if(i+d[i]-1>r) {
			l=i-d[i]+1;
			r=i+d[i]-1;
		}
	}
} 

int main(){
    scanf("%s",a+1);
    int n=strlen(a+1);
    int k=0;
    s[0]='$';
    s[++k]='#';
    for(int i=1;i<=n;i++){
    	s[++k]=a[i];s[++k]='#';
	}
	n=k;
	get_d(s,n);
	int ans=0;
	for(int i=1;i<=n;i++) ans=max(ans,d[i]);
	printf("%d",ans-1);
return 0;
}