Submission #1034941

#	Time	Username	Problem	Language	Result	Execution time	Memory
1034941		ArthuroWich	Mecho (IOI09_mecho)	C++17	100 / 100	130 ms	17400 KiB

mecho

#include <bits/stdc++.h>
using namespace std;
#define int long long int
int n, s;
char grid[805][805];
int hivedist[805][805], mechodist[805][805], vis[805][805];
vector<pair<int, int>> delta = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}}, hives;
pair<int, int> home, mecho;
bool valid(int i, int j) {
    return (i > 0 && j > 0 && i <= n && j <= n && (grid[i][j] == 'G' || grid[i][j] == 'H' || grid[i][j] == 'M'));
}
void hivebfs() {
    queue<pair<int, int>> q;
    for (auto c : hives) {
        q.push(c);
        hivedist[c.first][c.second] = 0;
    }
    while(!q.empty()) {
        auto [a, b] = q.front();
        q.pop();
        for (auto [dx, dy] : delta) {
            if (valid(a+dx, b+dy) && hivedist[a+dx][b+dy] > hivedist[a][b]+1) {
                hivedist[a+dx][b+dy] = hivedist[a][b]+1;
                q.push({a+dx, b+dy});
            }
        }
    }
}
bool check(int x) {
    if (hivedist[mecho.first][mecho.second] <= x) {
        return 0;
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            mechodist[i][j] = INT_MAX;
            vis[i][j] = 0;
        }
    }
    queue<pair<int, int>> q;
    q.push(mecho);
    mechodist[mecho.first][mecho.second] = 0;
    vis[mecho.first][mecho.second] = 1;
    while(!q.empty()) {
        auto [a, b] = q.front();
        q.pop();
        for (auto [dx, dy] : delta) {
            if (valid(a+dx, b+dy) && !vis[a+dx][b+dy] && (mechodist[a][b]+1)/s+x < hivedist[a+dx][b+dy]) {
                vis[a+dx][b+dy] = 1;
                mechodist[a+dx][b+dy] = mechodist[a][b]+1;
                q.push({a+dx, b+dy});
            }
        }
    }
    auto [a, b] = home;
    for (auto [dx, dy] : delta) {
        if (valid(a+dx, b+dy) && vis[a+dx][b+dy]) {
            return 1;
        }
    }
    return 0;
}
void solve() {
    cin >> n >> s;
    for (int i = 1; i <= n; i++) {
        string s;
        cin >> s;
        for (int j = 1; j <= n; j++) {
            grid[i][j] = s[j-1];
            mechodist[i][j] = INT_MAX;
            hivedist[i][j] = INT_MAX;
            if (s[j-1] == 'H') {
                hives.push_back({i, j});
            } else if (s[j-1] == 'M') {
                mecho = {i, j};
            } else if (s[j-1] == 'D') {
                home = {i, j};
            }
        }
    }    
    hivebfs();
    int l = 0, r = 1e8;
    while(l < r) {
        int m = (l+r+1)/2;
        if (check(m)) {
            l = m;
        } else {
            r = m-1;
        }
    }
    if (check(l)) {
        cout << l << endl;
    } else {
        cout << -1 << endl;
    }
}
int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    t = 1;
    while(t--) {
        solve();
    }
}

• Subtask 1: 100 / 100