Submission #168068

#	Time	Username	Problem	Language	Result	Execution time	Memory
168068		HungAnhGoldIBO2020	Palindromes (APIO14_palindrome)	C++14	15 / 100	632 ms	102280 KiB

palindrome

/*
abacaba
*/
#include<bits/stdc++.h>
#define int long long
#define hash hash1
using namespace std;
const int N=3e5+4;
const int mod=1610612741;
const int base=79;
int hash[N],rev_hash[N],mul[N],max1=1,sum[N];
map<int,int> cnt;
int gethash(int l,int r){
	return ((hash[r]-hash[l-1]*mul[r-l+1])%mod+mod)%mod;
}
int gethash_rev(int l,int r){
	return ((rev_hash[l]-rev_hash[r+1]*mul[r-l+1])%mod+mod)%mod;
}
struct node{
	int nxt[26],len,suf;
};
node Eer[N];
int sz=0,lst;
string s;
void add(int idx){
//	cout<<idx<<" BEGIN"<<endl;
	//special case idx=0
	int cha=(s[idx]-'a');
	if(idx==0){
		sz++;
		Eer[1].nxt[cha]=sz;
		Eer[sz].len=1;
		Eer[sz].suf=2;
		return;
	}
	while(idx-Eer[lst].len-1<=0||s[idx]!=s[idx-Eer[lst].len-1]){
		if(lst==1){
			break;
		}
		lst=Eer[lst].suf;
	}
	if(!Eer[lst].nxt[cha]){
		sz++;
		Eer[lst].nxt[cha]=sz;
		Eer[sz].len=Eer[lst].len+2;
		if(Eer[sz].len!=1){
			int sf=Eer[lst].suf;
			assert(idx-Eer[sf].len-1>0);
			while(s[idx]!=s[idx-Eer[sf].len-1]){
				sf=Eer[sf].suf;
			}
			Eer[sz].suf=Eer[sf].nxt[cha];
		}
		else{
			Eer[sz].suf=2;
		}
	}
	lst=Eer[lst].nxt[cha];
//	cout<<"LST "<<lst<<" LEN "<<Eer[lst].len<<" SUF "<<Eer[lst].suf<<endl;
//	cout<<"END"<<endl;
	return;
}
void build(string s1){
	sz=2;
	Eer[1].len=-1;
	Eer[1].suf=1;
	Eer[2].len=0;
	Eer[2].suf=1;
	lst=1;
	s=s1;
	for(int i=0;i<s.size();i++){
		add(i);
	}
}
void dfs(int x,int val){
	sum[x]=cnt[val];
	for(int i=0;i<26;i++){
		if(Eer[x].nxt[i]){
			if(Eer[x].len==-1){
				dfs(Eer[x].nxt[i],i+1);
			}
			else{
				dfs(Eer[x].nxt[i],(i+1 + val*base + (i+1)*mul[Eer[x].len+1])%mod);
			}
			sum[x]+=sum[Eer[x].nxt[i]];
		}
	}
	max1=max(max1,Eer[x].len*sum[x]);
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	string s1;
	cin>>s1;
	build(s1);
	int n=s1.size(),i,j,k,l;
	s1=" "+s1;
	mul[0]=1;
	for(i=1;i<=n;i++){
		hash[i]=(hash[i-1]*base+(s1[i]-'a'+1))%mod;
		mul[i]=(mul[i-1]*base)%mod;
	}
	for(i=n;i>0;i--){
		rev_hash[i]=(rev_hash[i+1]*base+(s1[i]-'a'+1))%mod;
	}
	for(i=1;i<=n;i++){
//		cout<<i<<endl;
		k=0;
		l=min(i-1,n-i);
		while(k<l){
			j=(k+l+1)>>1;
			if(gethash(i-j,i+j)==gethash_rev(i-j,i+j)){
				k=j;
			}
			else{
				l=j-1;
			}
		}
		cnt[gethash(i-k,i+k)]++;
		if(i<=n&&s1[i]==s1[i+1]){
			k=0;
			l=min(i-1,n-i-1);
			while(k<l){
				j=(k+l+1)>>1;
				if(gethash(i-j,i+1+j)==gethash_rev(i-j,i+1+j)){
					k=j;
				}
				else{
					l=j-1;
				}
			}
			cnt[gethash(i-k,i+1+k)]++;
		}
	}
	dfs(1,0);
	dfs(2,0);
	for(i=1;i<=n;i++){
		if(gethash(1,i)==gethash_rev(1,i)){
			max1=max(max1,i);
		}
	}
	cout<<max1;
}

Compilation message (stderr)

palindrome.cpp: In function 'void build(std::__cxx11::string)':
palindrome.cpp:71:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.size();i++){
              ~^~~~~~~~~

• Subtask 1: 0 / 8
• Subtask 2: 15 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 26
• Subtask 5: 0 / 27