Submission #564457

#	Time	Username	Problem	Language	Result	Execution time	Memory
564457		hoanghq2004	Portals (BOI14_portals)	C++14	100 / 100	354 ms	46552 KiB

portals

#include <bits/stdc++.h>

using namespace std;

int n, m;
char c[1010][1010];
pair <int, int> nxt[1010][1010][4], s, t;
int mx[4] = {-1, 0, 1, 0};
int my[4] = {0, -1, 0, 1};
int d[1010][1010];
int dist_to_wall[1010][1010];

void bfs() {
    queue <pair <int, int> > q;
    for (int i = 0; i <= n + 1; ++i)
        for (int j = 0; j <= m + 1; ++j)
            if (c[i][j] == '#') {
                dist_to_wall[i][j] = 0;
                q.push({i, j});
            }
            else dist_to_wall[i][j] = 1e9;
    while (!q.empty()) {
        int u = q.front().first;
        int v = q.front().second;
        q.pop();
        for (int i = 0; i < 4; ++i) {
            int x = u + mx[i], y = v + my[i];
            if (x < 0 || x > n + 1 || y < 0 || y > m + 1 || dist_to_wall[x][y] != 1e9) continue;
            dist_to_wall[x][y] = dist_to_wall[u][v] + 1;
            q.push({x, y});
        }
    }
}

void dijkstra() {
    priority_queue <pair <int, pair <int, int> > > pq;
    for (int i = 0; i <= n + 1; ++i)
        for (int j = 0; j <= m + 1; ++j)
            d[i][j] = 1e9;
    d[s.first][s.second] = 0;
    pq.push({0, s});
    while (!pq.empty()) {
        int u = pq.top().second.first;
        int v = pq.top().second.second;
        int dist = - pq.top().first;
        pq.pop();
        if (dist != d[u][v]) continue;
        for (int i = 0; i < 4; ++i) {
            int x = u + mx[i];
            int y = v + my[i];
            if (c[x][y] != '#' && d[x][y] > d[u][v] + 1) {
                d[x][y] = d[u][v] + 1;
                pq.push({- d[x][y], {x, y}});
            }
            x = nxt[u][v][i].first, y = nxt[u][v][i].second;
            if (d[u][v] + dist_to_wall[u][v] < d[x][y]) {
                d[x][y] = d[u][v] + dist_to_wall[u][v];
                pq.push({- d[x][y], {x, y}});
            }
        }
    }
}

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i <= n + 1; ++i)
        for (int j = 0; j <= m + 1; ++j)
            c[i][j] = '#';
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j)
            scanf(" %c", &c[i][j]);

    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j) {
            if (c[i][j] == 'S') s = {i, j};
            if (c[i][j] == 'C') t = {i, j};
        }
    for (int i = 1; i <= n; ++i)
        for (int j = 1; j <= m; ++j) {
            if (c[i - 1][j] == '#') nxt[i][j][2] = {i, j};
            else nxt[i][j][2] = nxt[i - 1][j][2];
            if (c[i][j - 1] == '#') nxt[i][j][3] = {i, j};
            else nxt[i][j][3] = nxt[i][j - 1][3];
        }
    for (int i = n; i >= 1; --i)
        for (int j = m; j >= 1; --j) {
            if (c[i + 1][j] == '#') nxt[i][j][0] = {i, j};
            else nxt[i][j][0] = nxt[i + 1][j][0];
            if (c[i][j + 1] == '#') nxt[i][j][1] = {i, j};
            else nxt[i][j][1] = nxt[i][j + 1][1];
        }
    bfs();
    dijkstra();
    cout << d[t.first][t.second];
}

Compilation message (stderr)

portals.cpp: In function 'int main()':
portals.cpp:65:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   65 |     scanf("%d%d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~
portals.cpp:71:18: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   71 |             scanf(" %c", &c[i][j]);
      |             ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 20 / 20
• Subtask 3: 20 / 20
• Subtask 4: 19 / 19
• Subtask 5: 30 / 30