UVA11624（bfs）

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstdlib>
  4 #include <cmath>
  5 #include <queue>
  6 #include <algorithm>
  7 #include <vector>
  8 #include <cstring>
  9 #include <stack>
 10 #include <cctype>
 11 #include <utility>
 12 #include <map>
 13 #include <string>
 14 #include <climits>
 15 #include <set>
 16 #include <string>
 17 #include <sstream>
 18 #include <utility>
 19 #include <ctime>
 20 using namespace std;
 21 const int MAXN(1010);
 22 const int MAXM(1000010);
 23 int fire[MAXN][MAXN];
 24 char g[MAXN][MAXN];
 25 bool vis[MAXN][MAXN];
 26 int fx[MAXM], fy[MAXM];
 27 int R, C, SX, SY;
 28 struct NODE
 29 {
 30     int x, y, val;
 31     NODE()
 32     {}
 33     NODE(int tx, int ty, int td): x(tx), y(ty), val(td)
 34     {}
 35 };
 36 
 37 int ok(int nx,int ny)
 38 {
 39     if(nx >= 1 && nx <= R && ny >= 1 && ny <= C )
 40         return 1;
 41     return 0;
 42 }
 43 int move_x[4] = {0, -1, 0, 1};
 44 int move_y[4] = {-1, 0, 1, 0};
 45 
 46 void bfs1(int n)///多个起点，超级源
 47 {
 48     queue<NODE> q;
 49     memset(fire+1, -1, sizeof(fire));
 50     for(int i = 0; i < n; ++i)///起点都压进去
 51     {
 52         q.push(NODE(fx[i], fy[i], 0));
 53         fire[fx[i]][fy[i]] = 0;
 54     }
 55     NODE cur;
 56     while(!q.empty())
 57     {
 58         cur = q.front();///从一个起点开始，然后四个方向扩散
 59         q.pop();
 60         for(int i = 0; i < 4; ++i)
 61         {
 62             int nx = cur.x+move_x[i], ny = cur.y+move_y[i];
 63             if(ok(nx,ny)&& g[nx][ny] != ‘#‘ && fire[nx][ny] == -1)
 64             {
 65                 fire[nx][ny] = cur.val+1;
 66                 q.push(NODE(nx, ny, cur.val+1));
 67                 ///重新做一个新的起点
 68             }
 69         }
 70     }
 71 }
 72 
 73 int bfs2()
 74 {
 75     queue<NODE> q;
 76     memset(vis+1, false, sizeof(vis[0])*R);
 77     q.push(NODE(SX, SY, 0));
 78     vis[SX][SY] = true;
 79     NODE cur;
 80     while(!q.empty())
 81     {
 82         cur = q.front();
 83         q.pop();
 84         if(cur.x == 1 || cur.y == 1 || cur.x == R || cur.y == C)
 85             return cur.val+1;
 86         for(int i = 0; i < 4; ++i)
 87         {
 88             int nx = cur.x+move_x[i], ny = cur.y+move_y[i];
 89             if(ok(nx,ny)&& g[nx][ny] != ‘#‘ && !vis[nx][ny] && (fire[nx][ny] == -1 || cur.val+1 < fire[nx][ny]))
 90             {
 91                 vis[nx][ny] = true;
 92                 q.push(NODE(nx, ny, cur.val+1));
 93             }
 94         }
 95     }
 96     return -1;
 97 }
 98 
 99 int main()
100 {
101     int T;
102     scanf("%d", &T);
103     while(T--)
104     {
105         scanf("%d%d", &R, &C);
106         int count = 0;
107         for(int i = 1; i <= R; ++i)
108         {
109             scanf("%s", g[i]+1);
110             for(int j = 1; j <= C; ++j)
111             {
112                 if(g[i][j] == ‘J‘)
113                 {
114                     SX = i;
115                     SY = j;
116                 }
117                 if(g[i][j] == ‘F‘)
118                 {
119                     fx[count] = i;
120                     fy[count++] = j;
121                 }
122             }
123         }
124         bfs1(count);
125         int ans = bfs2();
126         if(ans == -1)
127             printf("IMPOSSIBLE\n");
128         else
129             printf("%d\n", ans);
130     }
131     return 0;
132 }