1307-C, *1500

Problem - C - Codeforces

 

 

풀이

#include <bits/stdc++.h>
#define endl "\n"
#define ooop(i, n) for(int i = 0; i < n; i++)
#define loop(i, n) for(int i = 1; i <= n; i++)
#define all(v) (v).begin(), (v).end()
 
using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
 
ll i_j(int i, int j, map<int, vector<int> >& d)
{
    ll ret = 0;
    for(const auto l: d[i]){
        ret += d[j].end() - lower_bound(all(d[j]), l);
    }
    return ret;
}
 
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
 
    string s; cin >> s;
    map<int, vector<int> > d;
    ooop(i, s.size()) d[s[i]-'a'].emplace_back(i);
 
    ll res = 0;
    for(const auto& [_, v]: d){
        if(res < v.size()) res = v.size();
    }
    if(res == 1) cout << res << endl;
    else{
        res = ((res == 2)? 2: res*(res-1)/2);
        ooop(i, 26){
            ooop(j, 26){
                if(i == j) continue;
                res = max(res, i_j(i, j, d));
            }
        }
        cout << res << endl;
    }
 
    return 0;
}cs