Submission #499722

#	Time	Username	Problem	Language	Result	Execution time	Memory
499722		codr0	Palindromic Partitions (CEOI17_palindromic)	C++14	100 / 100	2058 ms	28580 KiB

palindromic

#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=a;i<=b;i++)
#define FORR(i,a,b) for(int i=a;i>=b;i--)
#define S second
#define F first
#define pb push_back
#define SZ(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define err(x) cout<<#x<<": "<<x<<'\n';
#define int long long
 
using namespace std;
const int MOD=98765431;
const int M=31;
	
	int pw(int a,int b){
		if(!b) return 1;
		int rt=pw(a,b/2);
		rt=(rt*rt)%MOD;
		if(b&1) rt=(rt*a)%MOD;
		return rt;
	}

	int inv(int x){
		return pw(x,MOD-2);
	}
	
	void Main(){
		int n;
		string s; cin>>s; n=SZ(s); s='$'+s;
		int ps[n+1]={};
		int PW[n+1];
		PW[0]=1;
		FOR(i,1,n) PW[i]=(PW[i-1]*M)%MOD;
		FOR(i,1,n){
			ps[i]=ps[i-1];
			ps[i]=(ps[i]+(((s[i]-'a'+1)*PW[i-1])%MOD))%MOD;
		}
		int l=1,r=n;
		int ans=0;
		while(r>l){
			int mid1=(r+l)/2;
			int mid2=mid1+1;
			if((r-l+1)&1)	mid1--;
			int t=-1;
			FOR(i,0,mid1-l){
				int hsh1=ps[i+l]-ps[l-1];
				hsh1=hsh1*inv(PW[l-1]); hsh1=((hsh1%MOD)+MOD)%MOD;
				int hsh2=ps[r]-ps[r-i-1];
				hsh2=hsh2*inv(PW[r-i-1]); hsh2=((hsh2%MOD)+MOD)%MOD;
				if(hsh1==hsh2) {t=i; break;}
			}
			if(t==-1) {
				ans++;
				break;
			}else{
				l=l+t+1;
				r=r-t-1;
				ans+=2;
			}
		}
		if(r==l) ans++;
		cout<<ans<<'\n';
	}

	int32_t main() {
	ios_base::sync_with_stdio(0); cin.tie(0);
	
	int T; cin>>T;
	while(T--) Main();

	return 0;
    }

Compilation message (stderr)

palindromic.cpp: In function 'void Main()':
palindromic.cpp:43:8: warning: unused variable 'mid2' [-Wunused-variable]
   43 |    int mid2=mid1+1;
      |        ^~~~

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 40 / 40