lswrc.cpp

#include <bits/stdc++.h>
#include <string>
#include <unordered_set>
#include <utility>
using namespace std;

typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<bool> vbl;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<string> vstr;
typedef vector<pll> vpll;

#define endl '\n'
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
constexpr ll mod = 1000000007;

inline void Parvez() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
}
template <class T> inline istream &operator>>(istream &in, vector<T> &v) {
    for (T &x : v) {
        in >> x;
    }
    return in;
}
template <class T> inline ostream &operator<<(ostream &out, vector<T> &v) {
    if (v.empty())
        return out;
    for (ll i = 0; i < v.size() - 1; i++) {
        out << v[i] << ' ';
    }
    out << v[v.size() - 1];
    return out;
}

string lswrc(string s) {
    unordered_set<char> st;
    ll l = 0, r = 0;
    pair<ll, ll> ans;
    while (r < s.size() and l < s.size()) {
        if (st.find(s[r]) == st.end()) {
            st.insert(s[r]);
            r++;
            if (r - l > ans.second - ans.first) {
                ans = {l, r};
            }
        } else {
            while (s[l] != s[r]) {
                st.erase(s[l]);
                l++;
            }
            st.erase(s[r]);
            l++;
        }
    }
    return s.substr(ans.first, ans.second - ans.first);
}
void solution(ll &T) {
    string s;
    cin >> s;
    cout << lswrc(s) << endl;
}

signed main() {
    Parvez();
    ll TT = 1;
    // cin>>TT;
    for (ll T = 1; T <= TT; T++)
        solution(T);
    return 0;
}