【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。

  1 /* 1813 */
  2 #include <iostream>
  3 #include <queue>
  4 #include <algorithm>
  5 #include <cstdio>
  6 #include <cstring>
  7 #include <cstdlib>
  8 using namespace std;
  9
 10 #define MAXN 80
 11 #define INF  0xffffff
 12
 13 int n, m;
 14 char ops[4][6] = {
 15     "east",
 16     "north",
 17     "south",
 18     "west"
 19 };
 20 int op[1005];
 21 int x[MAXN], y[MAXN];
 22 int dis[9][9];
 23 int visit[9][9];
 24 char map[9][9];
 25 int dir[4][2] = {
 26     0,1,-1,0,1,0,0,-1
 27 };
 28
 29 inline bool isEnd(int x, int y) {
 30     return x==0 || x==n-1 || y==0 || y==n-1;
 31 }
 32
 33 inline bool check(int x, int y) {
 34     return x<0 || x>=n || y<0 || y>=n;
 35 }
 36
 37 int bfs(int x, int y) {
 38     int xx, yy;
 39     int i, j, k;
 40     queue<int> Q;
 41
 42     k = 10*x + y;
 43     Q.push(k);
 44     memset(visit, -1, sizeof(visit));
 45     visit[x][y] = 0;
 46
 47     while (!Q.empty()) {
 48         k = Q.front();
 49         Q.pop();
 50         x = k/10;
 51         y = k%10;
 52         for (i=0; i<4; ++i) {
 53             xx = x + dir[i][0];
 54             yy = y + dir[i][1];
 55             if (map[xx][yy]==‘1‘ || visit[xx][yy]>=0)
 56                 continue;
 57             visit[xx][yy] = visit[x][y]+1;
 58             if (isEnd(xx, yy))
 59                 return visit[xx][yy];
 60             k = 10*xx + yy;
 61             Q.push(k);
 62         }
 63     }
 64     return 0;
 65 }
 66
 67 bool dfs(int d, int *px, int *py) {
 68     int mmax = -1;
 69     int x[MAXN], y[MAXN];
 70     int i, j, k;
 71
 72     for (i=0; i<m; ++i)
 73         mmax = max(mmax, dis[px[i]][py[i]]);
 74     if (mmax > d)
 75         return false;
 76     if (d == 0)
 77         return true;
 78
 79     for (i=0; i<4; ++i) {
 80         op[d] = i;
 81         for (j=0; j<m; ++j) {
 82             x[j] = px[j] + dir[i][0];
 83             y[j] = py[j] + dir[i][1];
 84             if (isEnd(px[j], py[j]) || map[x[j]][y[j]]==‘1‘) {
 85                 x[j] = px[j];
 86                 y[j] = py[j];
 87             }
 88         }
 89         if (dfs(d-1, x, y))
 90             return true;
 91     }
 92     return false;
 93 }
 94
 95 int main() {
 96     int t = 0;
 97     int i, j, k;
 98
 99     #ifndef ONLINE_JUDGE
100         freopen("data.in", "r", stdin);
101         freopen("data.out", "w", stdout);
102     #endif
103
104     while (scanf("%d",&n) != EOF) {
105         m = 0;
106         for (i=0; i<n; ++i)
107             scanf("%s", map[i]);
108         for (i=0; i<n; ++i) {
109             for (j=0; j<n; ++j) {
110                 if (map[i][j] == ‘1‘) {
111                     dis[i][j] = INF;
112                 } else {
113                     if (isEnd(i, j)) {
114                         dis[i][j] = 0;
115                     } else {
116                         dis[i][j] = bfs(i, j);
117                         x[m] = i;
118                         y[m] = j;
119                         ++m;
120                     }
121                 }
122             }
123         }
124         if (t++)
125             printf("\n");
126         if (m) {
127             for (i=1; ; ++i) {
128                 if (dfs(i, x, y))
129                     break;
130             }
131             for (j=i; j>0; --j)
132                 printf("%s\n", ops[op[j]]);
133         }
134     }
135
136     return 0;
137 }