Poj 3009 Curling 2.0【Dfs】

Curling 2.0

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 17391		Accepted: 7153

Description

On Planet MM-21, after their Olympic games this year, curling is getting popular. But the rules are somewhat different from ours. The game is played on an ice game board on which a square mesh is marked. They use only a single stone. The purpose of the game is to lead the stone from the start to the goal with the minimum number of moves.

Fig. 1 shows an example of a game board. Some squares may be occupied with blocks. There are two special squares namely the start and the goal, which are not occupied with blocks. (These two squares are distinct.) Once the stone begins to move, it will proceed until it hits a block. In order to bring the stone to the goal, you may have to stop the stone by hitting it against a block, and throw again.

Fig. 1: Example of board (S: start, G: goal)

The movement of the stone obeys the following rules:

· At the beginning, the stone stands still at the start square.

· The movements of the stone are restricted to x and y directions. Diagonal moves are prohibited.

· When the stone stands still, you can make it moving by throwing it. You may throw it to any direction unless it is blocked immediately(Fig. 2(a)).

· Once thrown, the stone keeps moving to the same direction until one of the following occurs:

o The stone hits a block (Fig. 2(b), (c)).

§ The stone stops at the square next to the block it hit.

§ The block disappears.

o The stone gets out of the board.

§ The game ends in failure.

o The stone reaches the goal square.

§ The stone stops there and the game ends in success.

· You cannot throw the stone more than 10 times in a game. If the stone does not reach the goal in 10 moves, the game ends in failure.

Fig. 2: Stone movements

Under the rules, we would like to know whether the stone at the start can reach the goal and, if yes, the minimum number of moves required.

With the initial configuration shown in Fig. 1, 4 moves are required to bring the stone from the start to the goal. The route is shown in Fig. 3(a). Notice when the stone reaches the goal, the board configuration has changed as in Fig. 3(b).

Fig. 3: The solution for Fig. D-1 and the final board configuration

Input

The input is a sequence of datasets. The end of the input is indicated by a line containing two zeros separated by a space. The number of datasets never exceeds 100.

Each dataset is formatted as follows.

the width(=w) and the height(=h) of the board 
First row of the board 
... 
h-th row of the board

The width and the height of the board satisfy: 2 <= w <= 20, 1 <= h <= 20.

Each line consists of w decimal numbers delimited by a space. The number describes the status of the corresponding square.

0	vacant square
1	block
2	start position
3	goal position

The dataset for Fig. D-1 is as follows:

6 6 
1 0 0 2 1 0 
1 1 0 0 0 0 
0 0 0 0 0 3 
0 0 0 0 0 0 
1 0 0 0 0 1 
0 1 1 1 1 1

Output

For each dataset, print a line having a decimal integer indicating the minimum number of moves along a route from the start to the goal. If there are no such routes, print -1 instead. Each line should not have any character other than this number.

Sample Input

2 1

3 2

6 6

1 0 0 2 1 0

1 1 0 0 0 0

0 0 0 0 0 3

0 0 0 0 0 0

1 0 0 0 0 1

0 1 1 1 1 1

6 1

1 1 2 1 1 3

6 1

1 0 2 1 1 3

12 1

2 0 1 1 1 1 1 1 1 1 1 3

13 1

2 0 1 1 1 1 1 1 1 1 1 1 3

0 0

Sample Output

1

4

-1

4

10

-1

Source

Japan 2006 Domestic

 

题目大意：给你一个n*m的图：

1是障碍

2是起点

3是终点

4是平地

小球一开始是静止的，只要选择了一个方向，就会一直向前去，直到碰到障碍1为止，然后障碍消失，小球变成静止的，问最少从2到3的步数。每一次从静止状态变成运动状态就算一步，并且，静止的时候不能撞障碍

思路：Dfs

1、因为有步数限制，而且地图不大，我们直接从起点Dfs即可。

2、我们分两种情况讨论，一种是当前状态为静止，那么我们就有4个方向可以去选择、分别讨论即可。另一种状态为运动中，如果下一步能够撞倒障碍，我们令障碍变成0，然后状态变成静止，当回溯回来的时候，我们令障碍再恢复。

AC代码：

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
int a[40][40];
int fx[4]={0,0,1,-1};
int fy[4]={1,-1,0,0};
int n,m,output;
void Dfs(int x,int y,int cur,int num)
{
    if(a[x][y]==3)
    {
        output=min(output,num);
    }
    if(num>10)return ;
    if(cur==-1)
    {
        for(int i=0;i<4;i++)
        {
            int xx=x+fx[i];
            int yy=y+fy[i];
            if(xx>=0&&xx<n&&yy>=0&&yy<m)
            {
                if(a[xx][yy]==2||a[xx][yy]==3||a[xx][yy]==0)
                {
                    Dfs(xx,yy,i,num+1);
                }
            }
        }
    }
    else
    {
        int xx=x+fx[cur];
        int yy=y+fy[cur];
        if(xx>=0&&xx<n&&yy>=0&&yy<m)
        {
            if(a[xx][yy]==2||a[xx][yy]==3||a[xx][yy]==0)
            {
                Dfs(xx,yy,cur,num);
            }
            if(a[xx][yy]==1)
            {
                a[xx][yy]=0;
                Dfs(x,y,-1,num);
                a[xx][yy]=1;
            }
        }
    }
}
int main()
{
    while(~scanf("%d%d",&m,&n))
    {
        memset(a,0,sizeof(a));
        if(n+m==0)break;
        int sx,sy;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                scanf("%d",&a[i][j]);
                if(a[i][j]==2)
                {
                    sx=i;
                    sy=j;
                }
            }
        }
        output=0x3f3f3f3f;
        Dfs(sx,sy,-1,0);
        if(output==0x3f3f3f3f)printf("-1\n");
        else
        printf("%d\n",output);
    }
}