Problem Name | EPALIN – Extend to Palindrome |
Judge | SPOJ |
Problem Link | https://www.spoj.com/problems/EPALIN/ |
Algorithms & DS | Prefix Function, KMP |
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
vector<ll>pi;
void ctPre(string s)
{
ll len=s.size();
pi.resize(len+5);
pi[0]=0;
for(ll i=1;i<len;i++){
ll j=pi[i-1];
while(j>0&&s[i]!=s[j])j=pi[j-1];
if(s[i]==s[j])j++;
pi[i]=j;
}
}
int main()
{
string s;
while(cin>>s){
ll len=s.size();
string pt=s;
reverse(pt.begin(),pt.end());
pt+="#";
pt+=s;
ll ptlen=pt.size();
ctPre(pt);
ll idx=len-pi[ptlen-1]-1;
cout<<s;
for(ll i=idx;i>=0;i--)cout<<s[i];
cout<<"\n";
}
}
Code language: PHP (php)