📦 ved015 / Codeforces-solution

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75// #include<bits/stdc++.h>
#include<iostream>
#include<vector>
#include<algorithm>
#include<map>
#include<set>
#include<string>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<long long> vll;
typedef vector<vector<ll> > vvll;

#define fastio() ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define pb push_back
#define mp make_pair
#define sz(x) ((int)(x).size())
#define all(x) x.begin(),x.end()

ll max(ll a, ll b, ll c){ return max(a, max(b, c));}
ll min(ll a, ll b, ll c){ return min(a, min(b, c));}
ll gcd(ll a, ll b) {if (b > a) {return gcd(b, a);} if (b == 0) {return a;} return gcd(b, a % b);}
ll fact(ll a) { return (a <= 1) ? 1 : a * fact(a - 1); }

vll factors(int n) { vll ans; int l = sqrt(n); for (int i = 1; i <= l; i++) { if (n % i == 0){ if (n/i == i) ans.pb(i); else {ans.pb(i); ans.pb(n/i);}}} return ans;}
string DecimalToBinary(ll num){string str; while(num){if(num & 1) str.pb('1');else str.pb('0');num>>=1;}return str;}
ll BinaryToDecimal(string num){ll ans = 0; ll base = 1; for (int i = sz(num) - 1; i >= 0; i--) {if (num[i] == '1') ans += base; base<<=1;}return ans;}

void Vedant(){
    string s;
    cin >> s;
    int n = sz(s);
    string temp = s;
    reverse(all(temp));

    pair<int,int> val = mp(0,-1); // {len,starting idx};
    int maxi = INT_MIN;
    pair<int,int> maxstring = mp(-1,-1); // {starting idx,ending idx}
    for(int i = 0; i < n; i++){
        if(s[i] == temp[n - i - 1]){
            int len = val.first;
            int idx = val.second;
            len++;
            if(idx == -1) idx = i;
            val = mp(len,idx);
        }
        else{
            if(val.first > maxi){
                maxi = val.first; 
                maxstring.first = val.second;
                maxstring.second = i;
            }
        }
    }

    int l = maxstring.first,r = maxstring.second;
    string ans = "";
    for(int i = l; i < r; i++){
        ans += s[i];
    }
    cout << ans << endl;
}


int main(){
    fastio();
    int t = 1;
    while(t--){
       Vedant();
    }
    return 0;
}