TLE 86pts 求调

#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ull=unsigned long long;
using ld=long double;
using pii=pair<int,int>;
#define fi first
#define se second
constexpr int N=2e5+5;
string s;
int n,d[N<<1],mx_bg[N<<1],mx_ed[N<<1];
string char_to_string(char ch) {
	string res="";
	res=res+ch;
	return res;
}
void manacher() {
	string str="";
	str.reserve(2*n+1);
	str+='#';
	for(int i=0;i<s.length();i++) {
		str+=s[i];
		str+='#';
	}
	for(int i=0,l=0,r=-1;i<2*n+1;i++) {
		int k=i>r?1:min(d[l+r-1],r-i+1);
		while(i-k>=0&&i+k<2*n+1&&str[i-k]==str[i+k]) k++;
		d[i]=k--;
		if(i+k>r) l=i-k,r=i+k;
		mx_bg[i-d[i]+1]=max(mx_bg[i-d[i]+1],d[i]-1);
		mx_ed[i+d[i]-1]=max(mx_ed[i+d[i]-1],d[i]-1);
	}
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin>>s;n=s.length();
	manacher();
	for(int i=2;i<2*n+1;i+=2) mx_bg[i]=max(mx_bg[i],mx_bg[i-2]-2);
	for(int i=2*n-2;i>=0;i-=2) mx_ed[i]=max(mx_ed[i],mx_ed[i+2]-2);
	int ans=0;
	for(int i=0;i<2*n+1;i+=2)
		if(mx_bg[i]&&mx_ed[i]) ans=max(ans,mx_bg[i]+mx_ed[i]);
	cout<<ans<<"\n";
	return 0;
}