POJ3009 Curling 2.0 （dfs入门题）

Time Limit:1000MS    Memory Limit:65536KB    64bit IO Format:%I64d & %I64u

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:
  • The stone hits a block (Fig. 2(b), (c)).
    • The stone stops at the square next to the block it hit.
    • The block disappears.
  • The stone gets out of the board.
    • The game ends in failure.
  • 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

---

这道题大意是一个在一个w*h的场地放一个冰壶（数字2），冰壶每次可以向一个方向滑，撞到冰（数字1）才能停下，且此时此冰破碎变成空地（数字0）。输出冰壶经过终点（数字3）最少要多少次（无法在10次内完成输出-1）。注意冰壶滑出界直接失败。

虽说是求最短次数但由于地图一直在变，还是用dfs比较好（由于最多允许滑10次所以不会超时），另外方向与行列也是经常弄混。。。反正这题建议和我一样练习dfs的新人可以做一做。

本人代码思路是提前预判停下的时机，在停下后判断前面遇到的是1，是3，亦或是地图边界，代码如下：

#include <iostream>
using namespace std;
#define N 10
int Map[22][22],Min;
int m,n;                                                            ///m横n竖
int dir[4][2]={{1,0},{0,1},{-1,0},{0,-1}};

int in(int x,int y){
    return x>=0&&y>=0&&x<m&&y<n;
}

void dfs(int x,int y,int cnt){
    if(cnt>=Min||cnt>N)return;
    int cx,cy,tx,ty;
    for(int i=0;i<4;i++){
        cx=dir[i][1];                                           ///选择一个方向
        cy=dir[i][0];
        tx=x;
        ty=y;
        if(!in(tx+cx,ty+cy)||Map[ty+cy][tx+cx]==1)                  ///无法移动
            continue;
        while(in(tx+cx,ty+cy)&&Map[ty+cy][tx+cx]==0){               ///移动
            tx+=cx;
            ty+=cy;
        }
        if(in(tx+cx,ty+cy)&&Map[ty+cy][tx+cx]==3){                  ///找到了终点
            Min=cnt;
            return;
        }
        if(in(tx+cx,ty+cy)&&Map[ty+cy][tx+cx]==1){                  ///碰到了墙壁
            Map[ty+cy][tx+cx]=0;
            dfs(tx,ty,cnt+1);
            Map[ty+cy][tx+cx]=1;
        }
        else ;                                                 ///碰到了地图边界
    }
}

int main(){
    int i,j,x,y;
    while(cin>>m>>n&&m+n){
        Min=11;
        for(i=0;i<n;i++){
            for(j=0;j<m;j++){
                cin>>Map[i][j];
                if(Map[i][j]==2)Map[y=i][x=j]=0;
            }
        }
        dfs(x,y,1);
        if(Min==11)cout<<-1<<endl;
        else cout<<Min<<endl;
    }
}