【HDOJ】1813 Escape from Tetris

bfs预处理一点到边界的最小距离，IDA*求出可行方案。注意按字典序初始化dir数组。并且存在中间点全为1，边界含0的可能性（wa了很多次）。此时不输出任何命令。

 /* 1813 */
 #include <iostream>
 #include <queue>
 #include <algorithm>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 using namespace std;

 #define MAXN 80
 #define INF  0xffffff

 int n, m;
 char ops[][] = {
     "east",
     "north",
     "south",
     "west"
 };
 int op[];
 int x[MAXN], y[MAXN];
 int dis[][];
 int visit[][];
 char map[][];
 int dir[][] = {
     ,,-,,,,,-
 };

 inline bool isEnd(int x, int y) {
     return x== || x==n- || y== || y==n-;
 }

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

 int bfs(int x, int y) {
     int xx, yy;
     int i, j, k;
     queue<int> Q;

     k = *x + y;
     Q.push(k);
     memset(visit, -, sizeof(visit));
     visit[x][y] = ;

     while (!Q.empty()) {
         k = Q.front();
         Q.pop();
         x = k/;
         y = k%;
         for (i=; i<; ++i) {
             xx = x + dir[i][];
             yy = y + dir[i][];
             if (map[xx][yy]=='' || visit[xx][yy]>=)
                 continue;
             visit[xx][yy] = visit[x][y]+;
             if (isEnd(xx, yy))
                 return visit[xx][yy];
             k = *xx + yy;
             Q.push(k);
         }
     }
     return ;
 }

 bool dfs(int d, int *px, int *py) {
     int mmax = -;
     int x[MAXN], y[MAXN];
     int i, j, k;

     for (i=; i<m; ++i)
         mmax = max(mmax, dis[px[i]][py[i]]);
     if (mmax > d)
         return false;
     if (d == )
         return true;

     for (i=; i<; ++i) {
         op[d] = i;
         for (j=; j<m; ++j) {
             x[j] = px[j] + dir[i][];
             y[j] = py[j] + dir[i][];
             if (isEnd(px[j], py[j]) || map[x[j]][y[j]]=='') {
                 x[j] = px[j];
                 y[j] = py[j];
             }
         }
         if (dfs(d-, x, y))
             return true;
     }
     return false;
 }

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

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

     while (scanf("%d",&n) != EOF) {
         m = ;
         for (i=; i<n; ++i)
             scanf("%s", map[i]);
         for (i=; i<n; ++i) {
             for (j=; j<n; ++j) {
                 if (map[i][j] == '') {
                     dis[i][j] = INF;
                 } else {
                     if (isEnd(i, j)) {
                         dis[i][j] = ;
                     } else {
                         dis[i][j] = bfs(i, j);
                         x[m] = i;
                         y[m] = j;
                         ++m;
                     }
                 }
             }
         }
         if (t++)
             printf("\n");
         if (m) {
             for (i=; ; ++i) {
                 if (dfs(i, x, y))
                     break;
             }
             for (j=i; j>; --j)
                 printf("%s\n", ops[op[j]]);
         }
     }

     return ;
 }