POJ 3322 Bloxorz I (bfs)

题意：一款著名的智力游戏：滚木块。输入地图，输出要完成目标最少的步数。

思路：求最少的步数，那么一般就要用BFS，思路很清晰，就是状态保存的时候要注意了，题目数据时500*500的矩阵，木块是3类状态，竖向的、横向的、站立的，因为存储空间的限制，就只能分开保存这三类状态...这类题一定要细心细心在细心.......

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <memory.h>
#include <cmath>
#include <bitset>
#include <queue>
#include <vector>
using namespace std;

const int BORDER = (1<<20)-1;
const int MAXSIZE = 37;
const int MAXN = 1010;
const int INF = 0x4ffffff;

#define CLR(x,y) memset(x,y,sizeof(x))
#define ADD(x) x=((x+1)&BORDER)
#define IN(x) scanf("%d",&x)
#define OUT(x) printf("%d\n",x)
#define MIN(m,v) (m)<(v)?(m):(v)
#define MAX(m,v) (m)>(v)?(m):(v)
#define ABS(x) ((x)>0?(x):-(x))

#define SET_NODE(no,a,b,c,d) {no.state=a,no.x=b,no.y=c,no.val=d;}

int n,m,ex,ey;
int ans;
bool visit[3][MAXN][MAXN];//0:oo 1:horizon 2:vertical
char g[MAXN][MAXN];

int dir[5][4][3]={
    {{0,0,0},{0,0,0},{0,0,0},{0,0,0}},
    {{-2,0,4},{1,0,4},{0,-2,2},{0,1,2}},
    {{-1,0,2},{1,0,2},{0,-1,1},{0,2,1}},
    {{0,0,0},{0,0,0},{0,0,0},{0,0,0}},
    {{-1,0,1},{2,0,1},{0,-1,4},{0,1,4}}};

typedef struct{
    int state;
    int x,y;
    int val;
}NODE;
NODE start_node;

int init()
{
    CLR(visit,0);
    CLR(g,0);
    ans = 0;
    return 0;
}
int input()
{
    int i,j,tmp,k;
    int pos[2][2];
    int tag = 0;
    for(i = 0; i < n; ++i)
        scanf("%s",g[i]);
    for(i = 0; i < n; ++i)
        for(j = 0; j < m; ++j)
        {
            if(g[i][j] != '#')
            {
                if(g[i][j] == 'X')
                {
                    pos[tag][0] = i;
                    pos[tag][1] = j;
                    ++tag;
                }
                else if(g[i][j] == 'O')
                {
                    g[i][j] = '.';
                    ex = i;
                    ey = j;
                }
            }
        }
    if(tag == 1)
    {
        SET_NODE(start_node,1,pos[0][0],pos[0][1],0);
        visit[0][start_node.x][start_node.y] = true;
        return 0;
    }
    if(pos[0][0] == pos[1][0])
    {
        tmp = MIN(pos[0][1],pos[1][1]);
        SET_NODE(start_node,2,pos[0][0],tmp,0);
        visit[1][start_node.x][start_node.y] = true;
        return 0;
    }
    if(pos[0][1] == pos[1][1])
    {
        tmp = MIN(pos[0][0], pos[1][0]);
        SET_NODE(start_node,4,tmp,pos[0][1],0);
        visit[2][start_node.x][start_node.y] = true;
    }
    return 0;
}
bool _in(const int& x,const int& y)
{
    if(x < 0 || x >= n || y < 0 || y >= m)
        return false;
    return true;
}
bool _check(const NODE& node)
{
    int x,y,a,b;
    if(node.x < 0 || node.y < 0)
        return false;
    if(node.state & 1)
    {
        if(!visit[0][node.x][node.y] && g[node.x][node.y] == '.')
        {
            visit[0][node.x][node.y] = true;
            return true;
        }
        else
            return false;
    }
    if(node.state & 2)
    {
        x = a = node.x;
        y = node.y;
        b = y + 1;
        if(visit[1][x][y])
            return false;
        if(g[x][y] == '#' || g[a][b] == '#')
            return false;
        visit[1][x][y] = true;
    }else
    {
        x = node.x;
        y = b = node.y;
        a = x + 1;
        if(visit[2][x][y])
            return false;
        if(g[x][y] == '#' || g[a][b] == '#')
            return false;
        visit[2][x][y] = true;
    }
    return true;
}
int bfs()
{
    int a,b,x,y,i,j,tmp;

    NODE t_node,node;
    queue<NODE> que;
    while(!que.empty())
        que.pop();
    que.push(start_node);
    while(!que.empty())
    {
        node = que.front();
        que.pop();

        if((node.state & 1) && node.x==ex && node.y==ey)
            return node.val;
        for(int i = 0; i < 4; ++i)
        {
            x = node.x + dir[node.state][i][0];
            y = node.y + dir[node.state][i][1];
            SET_NODE(t_node,dir[node.state][i][2],x,y,node.val+1);
            if(_check(t_node))
                que.push(t_node);
        }
    }
    return -1;
}
int work()
{
    ans = bfs();
    if(ans == -1)
        printf("Impossible\n");
    else
        printf("%d\n",ans);
    return 0;
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        if(!n && !m)
            break;
        init();
        input();
        work();
    }
    return 0;
}