https://codedrills.io/contests/icpc-amritapuri-2022-qualifier-mock-round/problems/red-and-blue

#include <bits/stdc++.h>

#define int long long

using namespace std;

signed main() {
    int t;
    cin >> t;

    while (t--) {

        int n;
        cin >> n;
        string s;
        cin >> s;
        vector<int> D;

        // taking inputs for the array D
        for (int i = 0; i < n; i++) {
            int temp;
            cin >> temp;
            D.push_back(temp);
        }

        // trying to count the min number of spills
        int i = 0;
        int maxSpill = -1;
        int count = 0;

        bool possible = true;

        while (i < n) {

            if (s[i] == 'B') {

                if (maxSpill >= i) {
                    int j = i;
                    while (j <= maxSpill && j < n) {
                        s[j] = 'R';
                        j++;
                    }
                    count++;
                } else {
                    cout << "-1"
                         << "\n";
                    possible = false;
                    break;
                }
            }

            if (D[i] + i > maxSpill) {
                maxSpill = D[i] + i;
            }
            i++;
        }

        // cout<<"String: "<<s<<"\n";

        if (possible) {
            cout << count << "\n";
        } else {
            continue;
        }
    }

    return 0;
}