【HDOJ】3500 Fling

题意巨难懂。简言之，就是球互相碰撞时，主动碰撞的球将会停止，另一个球将沿着碰撞方向继续移动，不断碰撞。但是无法弹射紧挨着的球，但是若a弹射b，bc相邻，这种情况b可以弹射c。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 using namespace std;

 #define MAXN 10

 typedef struct {
     int x, y;
     char d;
 } node_t;

 node_t nodes[];
 char map[MAXN][MAXN];
 int on;
 // U < L < R < D.
 int dir[][] = {-,,,-,,,,};

 bool check(int x, int y) {
     return x<||x>=||y<||y>=;
 }

 char getDir(int k) {
     if (k==) return 'U';
     if (k==) return 'L';
     if (k==) return 'R';
     return 'D';
 }

 bool dfs(int n) {
     int i, j, k, x, y;
     bool flag;

     if (n == )
         return true;

     for (i=; i<; ++i) {
         for (j=; j<; ++j) {
             if (map[i][j] == 'O') {
                 for (k=; k<; ++k) {
                     x = i + dir[k][];
                     y = j + dir[k][];
                     if (check(x, y) || map[x][y]=='O')
                         continue;
                     flag = false;
                     while (!check(x, y)) {
                         if (map[x][y] == 'O') {
                             flag = true;
                             map[x][y] = 'X';
                             map[x-dir[k][]][y-dir[k][]] = 'O';
                         }
                         x += dir[k][];
                         y += dir[k][];
                     }
                     if (flag) {
                         map[i][j] = 'X';
                         nodes[n].x = i;
                         nodes[n].y = j;
                         nodes[n].d = getDir(k);
                         if (dfs(n-))
                             return true;
                         do {
                             x -= dir[k][];
                             y -= dir[k][];
                             if (map[x][y] == 'O') {
                                 map[x][y] = 'X';
                                 map[x+dir[k][]][y+dir[k][]] = 'O';
                             }
                         } while (x!=i || y!=j);
                         map[i][j] = 'O';
                     }
                 }
             }
         }
     }

     return false;
 }

 int main() {
     int i = , j;
     int t = ;

 #ifndef ONLINE_JUDGE
     freopen("data.in", "r", stdin);
 #endif

     while (scanf("%s", &map[i]) != EOF) {
         for (i=; i<; ++i)
             scanf("%s", &map[i]);
         on = ;
         for (i=; i<; ++i)
             for (j=; j<; ++j)
                 if (map[i][j] == 'O')
                     ++on;
         dfs(on-);

         if (t != )
             printf("\n");
         printf("CASE #%d:\n", ++t);
         for(i=on-; i>=; --i)
             printf("%d %d %c\n", nodes[i].x, nodes[i].y, nodes[i].d);
         getchar();
         i = ;
     }

     return ;
 }