1896B - AB Flipping - CodeForces Solution

#include <bits/stdc++.h>
#include <iostream>
using namespace std;
#define TxtIO freopen("input.txt","r",stdin); freopen("output.txt","w",stdout);
void fast() {
    cin.tie(nullptr);
    cout.tie(nullptr);
    ios_base::sync_with_stdio(false);
}
int main()
{
    fast();
    int t;
    cin>>t;
    while(t--)
    {
        int n;
        string ss;
        cin>>n>>ss;
        int j=n-1, i=0;
        while(i<n && ss[i]== 'B') i++;
        while(j>=0 && ss[j]=='A') j--;
        cout<< max(0, j-i)<<"\n";
    }
    return 0;
}