Submission #1301872

#	Time	Username	Problem	Language	Result	Execution time	Memory
1301872		ericl23302	Mecho (IOI09_mecho)	C++20	100 / 100	154 ms	8736 KiB

mecho

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    vector<pii> directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};

    int n, s;
    cin >> n >> s;
    vector<string> grid(n);
    for (auto &i : grid) cin >> i;

    pii start, target;
    vector<pii> hives, trees;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            if (grid[i][j] == 'T')
                trees.emplace_back(i, j);
            else if (grid[i][j] == 'M')
                start = {i, j};
            else if (grid[i][j] == 'D')
                target = {i, j};
            else if (grid[i][j] == 'H')
                hives.emplace_back(i, j);
        }
    }

    vector<vector<int>> dist(n, vector<int>(n, 1e9));

    queue<pii> q;
    for (auto &i : hives) {
        dist[i.first][i.second] = 0;
        q.push(i);
    }

    while (!q.empty()) {
        pii cur = q.front();
        q.pop();

        for (pii direction : directions) {
            pii nxt = {cur.first + direction.first,
                       cur.second + direction.second};
            if (nxt.first < 0 || nxt.first >= n || nxt.second < 0 ||
                nxt.second >= n)
                continue;
            char nxtC = grid[nxt.first][nxt.second];
            if (nxtC == 'T' || nxtC == 'D') continue;
            if (dist[nxt.first][nxt.second] < 1e9) continue;
            dist[nxt.first][nxt.second] = dist[cur.first][cur.second] + 1;
            q.push(nxt);
        }
    }

    auto possible = [&](int shift) {
        if (dist[start.first][start.second] - shift <= 0) return false;
        vector<vector<int>> minSteps(n, vector<int>(n, 1e9));
        queue<pair<pii, int>> q2;
        q2.emplace(start, 0);
        minSteps[start.first][start.second] = 0;

        while (!q2.empty()) {
            auto [cur, steps] = q2.front();
            q2.pop();

            for (pii direction : directions) {
                pii nxt = {cur.first + direction.first,
                           cur.second + direction.second};
                if (nxt.first < 0 || nxt.first >= n || nxt.second < 0 ||
                    nxt.second >= n)
                    continue;
                char nxtC = grid[nxt.first][nxt.second];
                if (nxtC == 'T') continue;
                if (minSteps[nxt.first][nxt.second] < 1e9) continue;
                if (dist[nxt.first][nxt.second] - shift - (steps + 1) / s <= 0)
                    continue;
                minSteps[nxt.first][nxt.second] = steps + 1;
                q2.emplace(nxt, steps + 1);
            }
        }

        return (minSteps[target.first][target.second] < 1e9);
    };

    int least = 0, most = 1e6, best = -1;
    while (least <= most) {
        int mid = (least + most) / 2;
        if (possible(mid))
            best = max(best, mid), least = mid + 1;
        else
            most = mid - 1;
    }

    cout << best << endl;

    return 0;
}

• Subtask 1: 100 / 100