UVA11624-Fire! (Twice bfs), uva11624-firebfs

UVA11624-Fire! (Twice bfs), uva11624-firebfs

Question Link

Your task is to help J out of the maze of fire. J can be moved in four directions every minute, and all the fire grids will spread around. There are some obstacles in the maze, and J and fire cannot enter. When J walked to the border lattice of a maze, we thought he had walked out of the maze.

Idea: this is a big white question. In fact, you only need to deal with the fire time of each grid. For two BFS requests, the first time the grid is on fire, and the second BFS is used to determine whether the system can go out in the shortest time.

Code:

#include <iostream>#include <cstdio>#include <cstring>#include <queue>#include <algorithm>using namespace std;const int MAXN = 1005;const int INF = 0x3f3f3f3f;const int dx[] = {-1, 0, 0, 1};const int dy[] = {0, -1, 1, 0};struct node{    node (int xx, int yy, int dd) {        x = xx;         y = yy;        d = dd;    }    int x, y, d;};char g[MAXN][MAXN];int vf[MAXN][MAXN], vm[MAXN][MAXN], T[MAXN][MAXN];int r, c, sx, sy;queue<node> qf;void bfs_fire() {    while (!qf.empty()) {        node u = qf.front();         qf.pop();         node v = u;        for (int i = 0; i < 4; i++) {            int tx = u.x + dx[i];             int ty = u.y + dy[i];                  if (tx < 0 || tx >= r || ty < 0 || ty >= c || g[tx][ty] == '#') continue;            if (!vf[tx][ty]) {                vf[tx][ty] = 1;                 v.x = tx;                 v.y = ty;                v.d = u.d + 1;                T[tx][ty] = v.d;                qf.push(v);            }          }    }}int bfs_man() {    queue<node> qm;    while (!qm.empty()) qm.pop();     node s(sx, sy, 0);    qm.push(s);    memset(vm, 0, sizeof(vm));    vm[sx][sy] = 1;    while (!qm.empty()) {        node u = qm.front();         qm.pop();         if (u.x == 0 || u.x == r - 1 || u.y == 0 || u.y == c - 1)            return u.d + 1;        node v = u;        for (int i = 0; i < 4; i++) {            int tx = u.x + dx[i];             int ty = u.y + dy[i];             if (tx < 0 || tx >= r || ty < 0 || ty >= c || g[tx][ty] == '#') continue;            if (u.d + 1 >= T[tx][ty]) continue;            if (!vm[tx][ty]) {                vm[tx][ty] = 1;                 v.x = tx;                 v.y = ty;                v.d = u.d + 1;                qm.push(v);            }        }    }    return -1;}int main() {    int cas;     scanf("%d", &cas);    while (cas--) {        scanf("%d%d", &r, &c);        for (int i = 0; i < r; i++)            scanf("%s", g[i]);        while(!qf.empty())  qf.pop();        memset(vf, 0, sizeof(vf));        memset(T, INF, sizeof(T));        for (int i = 0; i < r; i++) {            for (int j = 0; j < c; j++) {                if (g[i][j] == 'J') {                    sx = i;                     sy = j;                 }                if (g[i][j] == 'F') {                    node tmp(i, j, 0);                           vf[i][j] = 1;                    T[i][j] = 0;                    qf.push(tmp);                }             }         }        bfs_fire();        int ans = bfs_man();            if (ans == -1)             printf("IMPOSSIBLE\n");        else             printf("%d\n", ans);    }    return 0;}