Algorithm/eating-snake/main.cc

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

//#define ENABLE_LOG

struct snake {
    int id;
    int power;

    snake(int id, int power) {
        this->id = id;
        this->power = power;
    }

    bool operator<(const snake &obj) const {
        if (obj.power == power) return obj.id < id;
        return obj.power < power;
    }

    bool operator>=(const snake &obj) const {
        return power >= obj.power;
    }
};

bool sort_by_id(snake a, snake b) {
    return b.id > a.id;
}

void eat(vector<snake> &vec, bool skip_sort = false) {
    if (vec.size() < 2) return;
    if (!skip_sort) {
        sort(vec.begin(), vec.end());
    }

#if defined(ENABLE_LOG)
    for (auto item: vec) {
        printf("eating log: \n");
        printf("(%d, %d)\n", item.id, item.power);
    }
#endif

    if (!(vec[0] >= vec[vec.size() - 1])) {
        return;
    }

    // If this snake ate the last snake
    snake curr = vec[0];
    snake last = vec[vec.size() - 1];
#if defined(ENABLE_LOG)
    printf("%d gonna to eat %d\n", curr.id, last.id);
#endif
    vec.pop_back();
    vec[0].power -= last.power;
    sort(vec.begin(), vec.end());
    if (vec[0].id != curr.id) {
        bool will_be_eaten = false;
        int strongest_curr_power = vec[0].power;
        // Looking up if current snake will be eaten
        for (auto it = vec.rbegin(); it < vec.rend(); it++) {
            if (strongest_curr_power >= it->power) {
                if (it->id == curr.id) {
                    // So bad, the new strongest snake will eat the current strongest snake
                    // Give up eating right now!
                    will_be_eaten = true;
                    break;
                }
                // No more thinking, just go for it
                strongest_curr_power -= it->power;
            }
        }

        if (will_be_eaten) {
#if defined(ENABLE_LOG)
            printf("%d give up, cuz it will be eaten after ate that snake, new strongest snake %d\n", curr.id,
                   vec[0].id);
#endif
            // It means the current snake going to be eaten
            // Revert the action
            for (auto &item: vec) {
                if (item.id == curr.id) {
                    item.power = curr.power;
                    break;
                }
            }
            vec.push_back(last);
            return;
        }
    }

#if defined(ENABLE_LOG)
    printf("%d has ate %d\n", curr.id, last.id);
#endif
    // Else, it means the current snake is still strong enough
    // Going to see other snakes can be eaten...
    return eat(vec, skip_sort = true);
}

int main() {
    int count;
    cin >> count;

    vector<snake> snakes;
    int t;
    cin >> t;
    for (int i = 0; i < t; i++) {
        int a;
        cin >> a;
        snakes.emplace_back(i + 1, a);
    }

    eat(snakes);
    cout << snakes.size() << endl;

    for (int i = 0; i < count - 1; i++) {
        int n;
        cin >> n;
        sort(snakes.begin(), snakes.end(), sort_by_id);
#if defined(ENABLE_LOG)
        printf("alter log: \n");
        for (const auto &item: snakes) {
            printf("%d ", item.id);
        }
        printf("\n");
#endif
        for (int j = 0; j < n; j++) {
            int id, alter;
            cin >> id >> alter;
            if (snakes.size() < id) {
                // Respawn
                snakes.emplace_back(id, alter);
            } else {
                // Alter power
                snakes[id - 1].power = alter;
            }
        }
        eat(snakes);
        cout << snakes.size() << endl;
    }
}