BFS(两点搜索) UVA 11624 Fire!

题目传送门

 /*
     BFS：首先对火搜索，求出火蔓延到某点的时间，再对J搜索，如果走到的地方火已经烧到了就不入队，直到走出边界。
 */
 /************************************************
 Author        :Running_Time
 Created Time  :2015-8-4 8:11:54
 File Name     :UVA_11624.cpp
 *************************************************/
 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;
 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 1e3 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 char maze[MAXN][MAXN];
 bool vis[MAXN][MAXN];
 int step[MAXN][MAXN];
 int dx[] = {-, , , };
 int dy[] = {, , -, };
 int n, m;
 bool judge_f(int x, int y)  {
     if (x <  || x > n || y <  || y > m || vis[x][y] || maze[x][y] == '#')    return false;
     return true;
 }
 bool judge_j(int x, int y)  {
     if (x <  || x > n || y <  || y > m)   return true;
     return false;
 }
 void BFS_F(void)  {
     memset (step, INF, sizeof (step));
     memset (vis, false, sizeof (vis));
     queue<pair<int, int> > Q;
     for (int i=; i<=n; ++i)    {
         for (int j=; j<=m; ++j)    {
             if (maze[i][j] == 'F') {
                 Q.push (make_pair (i, j));  vis[i][j] = true;
                 step[i][j] = ;
             }
         }
     }
     while (!Q.empty ()) {
         int x = Q.front ().first, y = Q.front ().second;    Q.pop ();
         for (int i=; i<; ++i) {
             int tx = x + dx[i], ty = y + dy[i];
             if (!judge_f (tx, ty))    continue;
             step[tx][ty] = step[x][y] + ;
             Q.push (make_pair (tx, ty));    vis[tx][ty] = true;
         }
     }
 }
 void BFS_J(void)    {
     memset (vis, false, sizeof (vis));
     queue<pair<int, int> > Q;
     for (int i=; i<=n; ++i)    {
         for (int j=; j<=m; ++j)    {
             if (maze[i][j] == 'J')  {
                 Q.push (make_pair (i, j)); step[i][j] = ; vis[i][j] = true;   break;
             }
         }
     }
     while (!Q.empty ()) {
         int x = Q.front ().first, y = Q.front ().second;    Q.pop ();
         for (int i=; i<; ++i) {
             int tx = x + dx[i], ty = y + dy[i];
             if (judge_j (tx, ty))    {
                 printf ("%d\n", step[x][y] + );    return ;
             }
             if (step[x][y] +  >= step[tx][ty] || vis[tx][ty] || maze[tx][ty] == '#') continue;
             Q.push (make_pair (tx, ty));    step[tx][ty] = step[x][y] + ;  vis[tx][ty] = true;
         }
     }
     puts ("IMPOSSIBLE");
 }
 int main(void)    {     //UVA 11624 Fire!
     int T;  scanf ("%d", &T);
     while (T--) {
         scanf ("%d%d", &n, &m);
         for (int i=; i<=n; ++i)    {
             scanf ("%s", maze[i] + );
         }
         BFS_F ();   BFS_J ();
     }
     return ;
 }