BFS(两点搜索) UVA 11624 Fire!

  1 /*
  2     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。
  3 */
  4 /************************************************
  5 Author        :Running_Time
  6 Created Time  :2015-8-4 8:11:54
  7 File Name     :UVA_11624.cpp
  8 *************************************************/
  9 
 10 #include <cstdio>
 11 #include <algorithm>
 12 #include <iostream>
 13 #include <sstream>
 14 #include <cstring>
 15 #include <cmath>
 16 #include <string>
 17 #include <vector>
 18 #include <queue>
 19 #include <deque>
 20 #include <stack>
 21 #include <list>
 22 #include <map>
 23 #include <set>
 24 #include <bitset>
 25 #include <cstdlib>
 26 #include <ctime>
 27 using namespace std;
 28 
 29 #define lson l, mid, rt << 1
 30 #define rson mid + 1, r, rt << 1 | 1
 31 typedef long long ll;
 32 const int MAXN = 1e3 + 10;
 33 const int INF = 0x3f3f3f3f;
 34 const int MOD = 1e9 + 7;
 35 char maze[MAXN][MAXN];
 36 bool vis[MAXN][MAXN];
 37 int step[MAXN][MAXN];
 38 int dx[4] = {-1, 1, 0, 0};
 39 int dy[4] = {0, 0, -1, 1};
 40 int n, m;
 41 
 42 bool judge_f(int x, int y)  {
 43     if (x < 1 || x > n || y < 1 || y > m || vis[x][y] || maze[x][y] == ‘#‘)    return false;
 44     return true;
 45 }
 46 
 47 bool judge_j(int x, int y)  {
 48     if (x < 1 || x > n || y < 1 || y > m)   return true;
 49     return false;
 50 }
 51 
 52 void BFS_F(void)  {
 53     memset (step, INF, sizeof (step));
 54     memset (vis, false, sizeof (vis));
 55     queue<pair<int, int> > Q;
 56     for (int i=1; i<=n; ++i)    {
 57         for (int j=1; j<=m; ++j)    {
 58             if (maze[i][j] == ‘F‘) {
 59                 Q.push (make_pair (i, j));  vis[i][j] = true;
 60                 step[i][j] = 0;
 61             }
 62         }
 63     }
 64     while (!Q.empty ()) {
 65         int x = Q.front ().first, y = Q.front ().second;    Q.pop ();
 66         for (int i=0; i<4; ++i) {
 67             int tx = x + dx[i], ty = y + dy[i];
 68             if (!judge_f (tx, ty))    continue;
 69             step[tx][ty] = step[x][y] + 1;
 70             Q.push (make_pair (tx, ty));    vis[tx][ty] = true;
 71         }
 72     }
 73 }
 74 
 75 void BFS_J(void)    {
 76     memset (vis, false, sizeof (vis));
 77     queue<pair<int, int> > Q;
 78     for (int i=1; i<=n; ++i)    {
 79         for (int j=1; j<=m; ++j)    {
 80             if (maze[i][j] == ‘J‘)  {
 81                 Q.push (make_pair (i, j)); step[i][j] = 0; vis[i][j] = true;   break;
 82             }
 83         }
 84     }
 85     while (!Q.empty ()) {
 86         int x = Q.front ().first, y = Q.front ().second;    Q.pop ();
 87         for (int i=0; i<4; ++i) {
 88             int tx = x + dx[i], ty = y + dy[i];
 89             if (judge_j (tx, ty))    {
 90                 printf ("%d\n", step[x][y] + 1);    return ;
 91             }
 92             if (step[x][y] + 1 >= step[tx][ty] || vis[tx][ty] || maze[tx][ty] == ‘#‘) continue;
 93             Q.push (make_pair (tx, ty));    step[tx][ty] = step[x][y] + 1;  vis[tx][ty] = true;
 94         }
 95     }
 96     puts ("IMPOSSIBLE");
 97 }
 98 
 99 int main(void)    {     //UVA 11624 Fire!
100     int T;  scanf ("%d", &T);
101     while (T--) {
102         scanf ("%d%d", &n, &m);
103         for (int i=1; i<=n; ++i)    {
104             scanf ("%s", maze[i] + 1);
105         }
106         BFS_F ();   BFS_J ();
107     }
108 
109     return 0;
110 }