Fastest Solution in C++

include

include

using namespace std;

int main(){ ios::sync_with_stdio(false); cin.tie(nullptr);

int n;
cin >> n;
cin.ignore();

string s;
cin >> s;

vector<int> freq(26); 

for(char c : s) ++freq[c - 'a'];

int max_len = 0;
for(char c1 = 'a'; c1 <= 'z'; ++c1) {
    if(freq[c1 - 'a'] == 0) continue;

    for(char c2 = c1 + 1; c2 <= 'z'; ++c2) {
        if(freq[c2 - 'a'] == 0) continue;
        if(abs(freq[c1 - 'a'] - freq[c2 - 'a']) > 1) continue;
        if(freq[c1 - 'a'] + freq[c2 - 'a'] < max_len) continue;

        char last = '\0'; int len = 0;

        for(char c : s) {
            if(c == last) { len = 0; break; }
            if(c != c1 && c != c2) continue;
            last = c; ++len;
        }

        max_len = max(max_len, len);
    }
}

cout << max_len << endl;

return 0;

}