Codeforces Round #733 (Div. 1 + Div. 2, based on VK Cup 2021 - Elimination (Engine))

A - Binary Decimal

int main() {
    IOS;
    for (cin >> _; _; --_) {
        cin >> n;
        for (k = 0; n; umax(k, n % 10), n /= 10);
        cout << k << '\n';
    }
    return 0;
}

B - Putting Plates

int main() {
    IOS;
    for (cin >> _; _; --_) {
        cin >> n >> m;
        string s(m, '0'), t(m, '0'), p(m, '0');
        for (int i = 0; i < m; i += 2)
            s[i] = '1';
        cout << s << '\n';
 
        t[0] = t.back() = '1';
        for (int i = 1; i < n - 1; ++i)
            cout << ((i & 1) || i == n - 2 ? p : t) << '\n';
        cout << s << "\n\n";
    }
    return 0;
}

C - Pursuit

二分, \(check\)是\(O(1)\)

bool check(VI& a, VI& b, int mid) {
    int k = (n + mid) / 4;
    if (n <= k)
        return 1;
    if (!k)
        return a.back() + 100 * mid - b.back() >= 0;
    if (k <= mid)
        return a.back() - a[k - 1] + 100 * mid - b.back() >= 0;
    return a.back() - a[k - 1] + 100 * mid - b.back() + b[k - mid - 1] >= 0;
}
 
int main() {
    IOS;
    for (cin >> _; _; --_) {
        cin >> n;
        VI a(n), b(n);
        for (auto &i : a) cin >> i;
        for (auto &i : b) cin >> i;
        sort(all(a)); sort(all(b));
        for (int i = 1; i < n; ++i)
            a[i] += a[i - 1], b[i] += b[i - 1];
        ll l = 0, r = n;
        while (l < r) {
            int mid = l + r >> 1;
            if (check(a, b, mid)) r = mid;
            else l = mid + 1;
        }
        cout << l << '\n';
    }
    return 0;
}

D - Secret Santa

先全部让\(b_i = a_i\), 统计每个人收到的礼物数\(c_i\)

然后再让所有\(c_i <= 1\)

就可以把人分成4堆

1. 收了礼物没送
2. 没收没送
3. 送了没收
4. 送了收了

不用考虑\(4\)

剩下的适配即可, 看代码注意分出前三堆人的顺寻, 和适配的顺序

int main() {
    IOS;
    for (cin >> _; _; --_) {
        cin >> n;
        VI a(n + 1), b(n + 1), c(n + 1);
        for (int i = 1; i <= n; ++i) {
            cin >> a[i];
            b[i] = a[i];
            ++c[a[i]];
        }
        VI x, y, z;
        for (int i = 1; i <= n; ++i)
            if (c[i] && c[a[i]] > 1) {
                --c[a[i]];
                b[i] = 0;
                x.emplace_back(i);
            }
        for (int i = 1; i <= n; ++i)
            if (c[i] == 0 && c[a[i]] > 1) {
                --c[a[i]];
                b[i] = 0;
                y.emplace_back(i);
            } else if (c[i] == 0)
                z.emplace_back(i);
        while (!y.empty()) {
            if (!z.empty()) {
                b[y.back()] = z.back();
                z.pop_back();
                z.emplace_back(y.back());
                y.pop_back();
            } else if (y.size() > 1) {
                x.emplace_back(y.back());
                y.pop_back();
                b[y.back()] = x.back();
                z.emplace_back(y.back());
                y.pop_back();
            } else {
                for (int i = 1; i <= n; ++i)
                    if (b[i]) {
                        b[y.back()] = b[i];
                        b[i] = y.back();
                        y.pop_back();
                        break;
                    }
            }
        }
        while (!x.empty()) {
            b[x.back()] = z.back();
            x.pop_back();
            z.pop_back();
        }
        k = 0;
        for (int i = 1; i <= n; ++i)
            k += a[i] == b[i];
        cout << k << '\n';
        for (int i = 1; i <= n; ++i)
            cout << b[i] << char(" \n"[i == n]);
    }
    return 0;
}

E - Minimax

分类讨论

看代码怎么分类输出答案就行了

int main() {
    IOS;
    for (cin >> _; _; --_) {
        cin >> s;
        map<char, int> cnt;
        for (auto& c : s) ++cnt[c];
 
        if (cnt.size() == 1) {
            cout << s << '\n';
            continue;
        }
        
        char f = 0;
        for (auto &i : cnt)
            if (i.second == 1) {
                f = i.first;
                break;
            }
        if (f) {
            cnt.erase(f);
            cout << f;
            while (!cnt.empty())
                if (cnt.begin()->second--)
                    cout << cnt.begin()->first;
                else
                    cnt.erase(cnt.begin());
            cout << '\n';
            continue;
        }
 
        if (cnt.begin()->second - 1 << 1 <= s.size()) {
            auto p = *cnt.begin();
            cnt.erase(cnt.begin());
            --p.second;
            cout << p.first;
            while (!cnt.empty()) {
                if (p.second)
                    cout << p.first, --p.second;
                --cnt.begin()->second;
                cout << cnt.begin()->first;
                if (cnt.begin()->second == 0)
                    cnt.erase(cnt.begin());
            }
            if (p.second)
                cout << p.first;
            cout << '\n';
            continue;
        }
 
        if (cnt.size() == 2) {
            auto p = *cnt.begin();
            cnt.erase(cnt.begin());
            --p.second;
            cout << p.first;
            while (cnt.begin()->second--)
                cout << cnt.begin()->first;
            while (p.second--)
                cout << p.first;
            cout << '\n';
            continue;
        }
 
        pair<char, int> p = *cnt.begin();
        cnt.erase(cnt.begin());
        cout << p.first << cnt.begin()->first;
        for (--p.second; p.second; --p.second)
            cout << p.first;
        p = *cnt.begin();
        cnt.erase(cnt.begin());
        cout << cnt.begin()->first;
        --cnt.begin()->second;
        cnt[p.first] = p.second - 1;
        while (!cnt.empty())
            if (cnt.begin()->second--)
                cout << cnt.begin()->first;
            else
                cnt.erase(cnt.begin());
        cout << '\n';
    }
    return 0;
}