877B - Nikita and string - CodeForces Solution

#include <bits/stdc++.h>
 
using namespace std;
 
int prefa[5001], prefb[5001];
 
int main()
{
    string s;
    cin >> s;
    int num = 0;
    int n = s.size();
    for(int i = 1; i <= n; i++)
    {
        prefa[i] = prefa[i - 1] + (s[i - 1] == 'a');
        prefb[i] = prefb[i - 1] + (s[i - 1] == 'b');
    }
    int maxim = 0;
    for(int i = 0; i <= n; i++)
    {
        for(int j = i; j <= n; j++)
        {
            maxim = max(maxim, prefa[i] + (prefb[j] - prefb[i]) + (prefa[n] - prefa[j]));
        }
    }
    cout << maxim;
    return 0;
}