Submission #941118

#	Time	Username	Problem	Language	Result	Execution time	Memory
941118		Ghulam_Junaid	Portals (BOI14_portals)	C++17	100 / 100	279 ms	51684 KiB

portals

#include <bits/stdc++.h>
using namespace std;

const int N = 1e3 + 10;
const int inf = 1e9 + 10;

int n, m, sx, sy, ex, ey, dist[N][N];
char mat[N][N];

int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
//           U  R  D   L

vector<pair<int, int>> walls;
pair<int, int> max_move[N][N][4];
int wall_dist[N][N];

bool valid(int x, int y){
    return (x >= 0 and x < n and y >= 0 and y < m and mat[x][y] != '#');
}

void bfs(){
    for (int i = 0; i < n; i ++)
        for (int j = 0; j < m; j ++)
            wall_dist[i][j] = min(min(i + 1, j + 1), min(n - i, m - j));

    queue<pair<int, int>> q;
    for (auto [x, y] : walls){
        wall_dist[x][y] = 0;
        q.push({x, y});
    }

    while (!q.empty()){
        auto p = q.front();
        q.pop();

        int x = p.first;
        int y = p.second;

        for (int d = 0; d < 4; d ++){
            int nx = x + dx[d];
            int ny = y + dy[d];

            if (valid(nx, ny) and wall_dist[nx][ny] > wall_dist[x][y] + 1){
                wall_dist[nx][ny] = wall_dist[x][y] + 1;
                q.push({nx, ny});
            }
        }
    }
}

void dijkstra(){
    for (int i = 0; i < n; i ++)
        for (int j = 0; j < m; j ++)
            dist[i][j] = inf;
    dist[sx][sy] = 0;

    set<pair<int, pair<int, int>>> st;
    st.insert({0, {sx, sy}});

    while (!st.empty()){
        auto X = *st.begin();
        st.erase(st.begin());
        
        int cur = X.first;
        auto p = X.second;

        int x = p.first;
        int y = p.second;

        for (int d = 0; d < 4; d ++){
            int nx = x + dx[d];
            int ny = y + dy[d];

            if (valid(nx, ny) and dist[nx][ny] > dist[x][y] + 1){
                st.erase({dist[nx][ny], {nx, ny}});
                dist[nx][ny] = dist[x][y] + 1;
                st.insert({dist[nx][ny], {nx, ny}});
            }

            p = max_move[x][y][d];
            nx = p.first;
            ny = p.second;

            if (dist[nx][ny] > dist[x][y] + wall_dist[x][y]){
                st.erase({dist[nx][ny], {nx, ny}});
                dist[nx][ny] = dist[x][y] + wall_dist[x][y];
                st.insert({dist[nx][ny], {nx, ny}});
            }
        }
    }
}

int main(){
    cin >> n >> m;
    for (int i = 0; i < n; i ++){
        for (int j = 0; j < m; j ++){
            cin >> mat[i][j];
            if (mat[i][j] == 'S')
                sx = i, sy = j;
            if (mat[i][j] == 'C')
                ex = i, ey = j;
            if (mat[i][j] == '#')
                walls.push_back({i, j});
        }
    }

    bfs();

    for (int i = 0; i < n; i ++){
        for (int j = 0; j < m; j ++){
            if (mat[i][j] == '#')
                continue;

            if (valid(i - 1, j))
                max_move[i][j][0] = max_move[i - 1][j][0];
            else
                max_move[i][j][0] = {i, j};

            if (valid(i, j - 1))
                max_move[i][j][3] = max_move[i][j - 1][3];
            else
                max_move[i][j][3] = {i, j};
        }
    }

    for (int i = n - 1; i >= 0; i --){
        for (int j = m - 1; j >= 0; j --){
            if (mat[i][j] == '#')
                continue;

            if (valid(i + 1, j))
                max_move[i][j][2] = max_move[i + 1][j][2];
            else
                max_move[i][j][2] = {i, j};

            if (valid(i, j + 1))
                max_move[i][j][1] = max_move[i][j + 1][1];
            else
                max_move[i][j][1] = {i, j};
        }
    }

    dijkstra();
    cout << dist[ex][ey] << endl;
}

Compilation message (stderr)

portals.cpp: In function 'void dijkstra()':
portals.cpp:65:13: warning: unused variable 'cur' [-Wunused-variable]
   65 |         int cur = X.first;
      |             ^~~

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