空洞法递归误差

Question

static int x,y,fx,fy;
static char g[][]={ //your maze array , # represents wall and . represents path};
static Stack<Integer>stackx=new Stack<Integer>();
static Stack<Integer>stacky=new Stack<Integer>();
// both of the stacks are used for reverting changes int he maze to original
public static void main(String args[])
{
    x=y=0;
		for(int i=0;i<g.length;i++)
		{
			for(int j=0;j<g[i].length;j++)
			{
				if(g[i][j]=='S')
				{
					x=j;
					y=i;
				}
				else if(g[i][j]=='G')
				{
					fx=j;
					fy=i;
				}
			}
		}
    rec(x,y);
    System.out.println("HEllooooooo");
}
public static void rec(int x,int y)
{
   try
   {
       System.out.println(x+" "+y+" "+check);
       if(x==fx && y==fy)
       {
           System.out.println("YES");
           check=true;
           x=y=0;
           return;
       }
       System.out.println(x+" "+y+" "+check);
       if(check==false)
       {
                         revert();// reverts maze back to original
		 change(); // slides walls in the maze
	
		for(int i=0;i<g.length;i++)
		{
			for(int j=0;j<g[0].length;j++)
			{
				System.out.print(g[i][j]);
			}
			System.out.println("");
		}
		if(!valid(x,y+1))
		{
			if(!((y+1)>(g.length-1)))
			{
				g[y+1][x]='#';
			}
		}
		else
		{
			rec(x,y+1);
		}
		if(!valid(x+1,y))
		{
			if(!((x+1)>(g[0].length-1)))
			{
				g[y][x+1]='#';
			}
		}
		else
		{
			rec(x+1,y);
		}
		if(!valid(x-1,y))
		{
			if(!((x-1)>=0))
			{
				g[y][x-1]='#';
			}
		}
		else
		{
			rec(x-1,y);
		}
		if(!valid(x,y-1))
		{
			if(!((y-1)>=0))
			{
				g[y-1][x]='#';
			}
		}
		else
		{
			rec(x,y-1);
		}
       }
    }catch(ArrayIndexOutOfBoundsException e)
     {
        System.out.println("NO");
        return;
     }
}

输出如下

4 1 false
YES      // output is correct and should end but it continues//
2 1 true //x and y values change from 4,1 to 2,1 even with no code to manipulate them
2 1 true
3 0 true
3 0 true
4 0 true
4 0 true
NO
1 1 true
1 1 true
0 1 true
0 1 true
NO
HEllooooooo

Answer 1

如果击中fx，fy是最终目标，那么：

boolean rec( int x, int y )

在打印“是”之后：

return true;

所有递归调用rec（...,...）都应该替换为

if( rec( ..., ... ) ) return true;

return false;