HDU1885 Key Task(BFS+状态压缩)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int MAX=100+10;
struct point
{
int x,y,step,state;
point(int x=0,int y=0,int step=0,int state=0):x(x),y(y),step(step),state(state){};
};
char g[MAX][MAX];
int vis[MAX][MAX][20];
int dirx[4]={0,1,0,-1};
int diry[4]={1,0,-1,0};
int n,m;
int sx,sy;
bool judgein(int x,int y)
{
return 0<=x&&x<n&&0<=y&&y<m;
}
int tran(char c)
{
if(c=='B'||c=='b') return 0;
if(c=='G'||c=='g') return 1;
if(c=='Y'||c=='y') return 2;
if(c=='R'||c=='r') return 3;
}
int bfs()
{
memset(vis,0,sizeof(vis));
queue<point> que;
vis[sx][sy][0]=1;
que.push(point(sx,sy,0,0));
while(!que.empty())
{
point top=que.front();
que.pop();
int x=top.x;
int y=top.y;
int step=top.step;
int state=top.state;
if(g[x][y]=='X')
{
return step;
}
for(int i=0;i<4;i++)
{
int nx=x+dirx[i];
int ny=y+diry[i];
int nstep=step+1;
int nstate=state;
if(judgein(nx,ny)&&g[nx][ny]!='#'&&!vis[nx][ny][nstate])
{
if(g[nx][ny]=='.'||g[nx][ny]=='X')
{
vis[nx][ny][nstate]=1;
que.push(point(nx,ny,nstep,nstate));
}
else if(g[nx][ny]>='A'&&g[nx][ny]<='Z')
{
int key=nstate&(1<<(tran(g[nx][ny])));
if(key)
{
vis[nx][ny][nstate]=1;
que.push(point(nx,ny,nstep,nstate));
}
}
else if(g[nx][ny]>='a'&&g[nx][ny]<='z')
{
nstate=nstate|(1<<(tran(g[nx][ny])));
vis[nx][ny][nstate]=1;
que.push(point(nx,ny,nstep,nstate));
}
}
}
}
return 0;
}
int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
while(scanf("%d%d",&n,&m))
{
if(n==0&&m==0) break;
getchar();
for(int i=0;i<n;i++)
{
for(int j=0;j<m;j++)
{
scanf("%c",&g[i][j]);
if(g[i][j]=='*')
{
sx=i;
sy=j;
g[i][j]='.';
}
}
getchar();
}
/*        for(int i=0;i<n;i++)
{
for(int j=0;j<m;j++)
{
printf("%c",g[i][j]);
}
printf("\n");
}
printf("%d %d\n",sx,sy);*/
int ans=bfs();
if(ans)
{
printf("Escape possible in %d steps.\n",ans);
}
else
{
printf("The poor student is trapped!\n");
}
}
return 0;
}