HDU 1475 Pushing Boxes

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <cmath>
  5 #include <algorithm>
  6 #include <climits>
  7 #include <vector>
  8 #include <queue>
  9 #include <cstdlib>
 10 #include <string>
 11 #include <set>
 12 #include <stack>
 13 #define LL long long
 14 #define pii pair<int,int>
 15 #define INF 0x3f3f3f3f
 16 using namespace std;
 17 const int maxn = 30;
 18 struct stats{
 19     int px,py,bx,by;
 20     string path;
 21 };
 22 struct node{
 23     int x,y;
 24     string path;
 25 };
 26 char mp[maxn][maxn];
 27 int r,c,box_x,box_y,pson_x,pson_y;
 28 string ans;
 29 const int dir[4][2] = {0,-1,0,1,-1,0,1,0};
 30 const char dc[4] = {‘W‘,‘E‘,‘N‘,‘S‘};
 31 const char dc2[4] = {‘w‘,‘e‘,‘n‘,‘s‘};
 32 bool check(int x,int y){
 33     return mp[x][y] != ‘#‘;
 34 }
 35 bool bfs2(int nx,int ny,int tx,int ty,int kx,int ky,string &pans){
 36     queue<node>q;
 37     bool vis[maxn][maxn] = {false};
 38     vis[nx][ny] = vis[kx][ky] = true;
 39     node now,tmp;
 40     now.x = nx;
 41     now.y = ny;
 42     now.path = "";
 43     q.push(now);
 44     while(!q.empty()){
 45         now = q.front();
 46         q.pop();
 47         if(now.x == tx && now.y == ty){
 48             pans = now.path;
 49             return true;
 50         }
 51         for(int i = 0; i < 4; i++){
 52             int zx = now.x + dir[i][0];
 53             int zy = now.y + dir[i][1];
 54             if(check(zx,zy)&&!vis[zx][zy]){
 55                 vis[zx][zy] = true;
 56                 tmp.x = zx;
 57                 tmp.y = zy;
 58                 tmp.path = now.path + dc2[i];
 59                 q.push(tmp);
 60             }
 61         }
 62     }
 63     return false;
 64 }
 65 bool bfs(){
 66     queue<stats>q;
 67     bool vis[maxn][maxn] = {false};
 68     vis[box_x][box_y] = true;
 69     stats tmp,now;
 70     now.px = pson_x;
 71     now.py = pson_y;
 72     now.bx = box_x;
 73     now.by = box_y;
 74     now.path = "";
 75     q.push(now);
 76     while(!q.empty()){
 77         now = q.front();
 78         q.pop();
 79         for(int i = 0; i < 4; i++){
 80             int nx = now.bx + dir[i][0];
 81             int ny = now.by + dir[i][1];
 82             int tx = now.bx - dir[i][0];
 83             int ty = now.by - dir[i][1];
 84             string pans = "";
 85             if(check(nx,ny)&&check(tx,ty)&&!vis[nx][ny]){
 86                 if(bfs2(now.px,now.py,tx,ty,now.bx,now.by,pans)){
 87                     vis[nx][ny] = true;
 88                     tmp.px = now.bx;
 89                     tmp.py = now.by;
 90                     tmp.bx = nx;
 91                     tmp.by = ny;
 92                     tmp.path = now.path + pans + dc[i];
 93                     if(mp[nx][ny] == ‘T‘){
 94                         ans = tmp.path;
 95                         return true;
 96                     }
 97                     q.push(tmp);
 98                 }
 99             }
100         }
101     }
102     return false;
103 }
104 int main(){
105     int cs = 1;
106     while(~scanf("%d %d",&r,&c) && r + c){
107         memset(mp,‘#‘,sizeof(mp));
108         getchar();
109         for(int i = 1; i <= r; i++){
110             for(int j = 1; j <= c; j++){
111                 mp[i][j] = getchar();
112                 if(mp[i][j] == ‘B‘){
113                     box_x = i;
114                     box_y = j;
115                 }
116                 if(mp[i][j] == ‘S‘){
117                     pson_x = i;
118                     pson_y = j;
119                 }
120             }
121             getchar();
122         }
123         printf("Maze #%d\n", cs++);
124         if(bfs()) cout<<ans<<endl;
125         else puts("Impossible.");
126         puts("");
127     }
128     return 0;
129 }