TLE: HDOJ 1010 Tempter of the Bone

超时了，dfs写的是对的（通过了discuss中一块强大的数据）

# include <stdio.h>
# include <string.h>


typedef struct{
    int x, y;
}Point;

const Point d[4] = {{-1,0}, {0,1}, {0,-1}, {1,0}};

int N, M, T, tot, ok;
char m[8][8];

int dfs(Point s, int dir);
int can_move(Point s, int dir);
void solve(Point s, Point e, int T);

int main()
{
    int i;
    char *p;
    Point s, e;
    
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    
    while (1)
    {
        scanf("%d%d%d", &N, &M, &T);
        if (!N && !M && !T) break;
        
        memset(m, 0, sizeof(m));
        
        for ( i = 1; i <= N; ++i)
        {
            scanf("%s", m[i]+1);
            if ((p = strchr(m[i]+1, 'S')) != NULL) {s.x = i; s.y = p-m[i];}
             if ((p = strchr(m[i]+1, 'D')) != NULL) {e.x = i; e.y = p-m[i];}
           }
           
           solve(s, e, T);
    }
    
    return 0;
}


int dfs(Point s, int dir)
{
    int ddir, f;
    
    f = 0;
    ++tot;
    s.x = s.x + d[dir].x;
    s.y = s.y + d[dir].y;
    if (m[s.x][s.y] == 'D') f = 1;
    if (tot == T && f) return ok = 1;
    m[s.x][s.y] = 'L';
    for ( ddir = 0; ddir < 4; ++ddir)
    {
         if (ddir != 3-dir && can_move(s, ddir))
            dfs(s, ddir);
    }
    --tot;
    if (!f)m[s.x][s.y] = '.';
    else m[s.x][s.y] = 'D';
}

int can_move(Point s, int dir)
{
    Point nx; 
    nx.x = s.x + d[dir].x;
    nx.y = s.y + d[dir].y;
    if (1 <= nx.x && nx.x <= N && 1 <= nx.y && nx.y <= M && (m[nx.x][nx.y] == '.' || m[nx.x][nx.y] == 'D'))
        return 1;       
       return 0;
}

void solve(Point s, Point e, int T)
{
    int dir;
    
    if (T >= N*M) {printf("NO\n"); return ;}
    if (m[s.x][s.y] == 'D')
    {
        if (T == 0) printf("YES\n");
        else printf("NO\n");
        return ;
    }
    m[s.x][s.y] = 'L';
    for (ok = dir = 0; dir < 4; ++dir)
    {
           tot = 0;
        if (can_move(s, dir) && !ok)
        {
            dfs(s, dir);
        }
    }
    printf(ok==1 ? "YES\n":"NO\n");
}