明天有空就写题解，不得不说 $CSDN$ 的界面越来越拉了

A. Red Versus Blue

#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t -- ) {
        int n, r, b;
        cin >> n >> r >> b;
        while (b) {
            int cnt = r / (b + 1);
            for (int i = 1; i <= cnt; i ++ )
                cout << "R";
            cout << "B";
            b --;
            r -= cnt;
        }
        for (int i = 1; i <= r; i ++ )
            cout << "R";
        cout << endl;
    }
	return 0;
}

B. Bit Flipping

#include <bits/stdc++.h>
using namespace std;
#define PB push_back
typedef vector<int> VI;
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t -- ) {
        int n, k;
        cin >> n >> k;
        string str;
        cin >> str;
        int tmp = 0;
        VI ans, res;
        for (int i = 0; i < str.size(); i ++ ) {
            if (i != str.size() - 1) {
                if (str[i] == '0') {
                    if (k & 1) {
                        ans.PB(1);
                        res.PB(0);
                    }
                    else if (tmp < k) {
                        ans.PB(1);
                        res.PB(1);
                        tmp ++;
                    } else {
                        ans.PB(0);
                        res.PB(0);
                    }
                } else {
                    if ((k & 1) && (tmp < k)) {
                        ans.PB(1);
                        res.PB(1);
                        tmp ++;
                    } else if ((k & 1)) {
                        ans.PB(0);
                        res.PB(0);
                    }
                    else {
                        ans.PB(1);
                        res.PB(0);
                    }
                }
            } else {
                if (tmp & 1) {
                    ans.PB((str[i] - '0') ^ 1);
                } else ans.PB(str[i] - '0');
                res.PB(k - tmp);
            }
        }
        for (auto t : ans) cout << t;
        cout << endl;
        for (auto t : res)
            cout << t << ' ';
        cout << endl;
    }
	return 0;
}

C. Line Empire

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const LL LNF = 0x3f3f3f3f3f3f3f3f;
const int N = 2e5 + 10;
int x[N];
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t -- ) {
        int n, a, b;
        cin >> n >> a >> b;
        LL num = LNF;
        LL sum = 0;
        for (int i = 1; i <= n; i ++ ) {
            cin >> x[i];
            sum += x[i];
        }
        LL res = 0;
        for (int i = 1; i <= n; i ++ ) {
            res += x[i];
            num = min(num, 1ll * b * x[i] + 1ll * a * x[i]
                + 1ll * (sum - res) * b - 1ll * b * (n - i) * x[i]);
        }
        num = min(num, b * sum);
        cout << num << endl;
    }
	return 0;
}

D. Reverse Sort Sum

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
int c[N], a[N];
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t -- ) {
        int n;
        cin >> n;
        LL sum = 0;
        for (int i = 0; i < n; i ++ ) 
            cin >> c[i];
        for (int i = 0; i < n; i ++ ) a[i] = 1;
        for (int i = 0; i < n; i ++ ) {
            if (c[i] == 0) a[i] = 0;
            else if (c[i] < n) a[c[i]] = 0, c[c[i]] += c[i];
        }
        for (int i = 0; i < n; i ++ ) cout << a[i] << ' ';
        cout << endl;
    }
	return 0;
}