Exception class is as follows:

 static class Point {
Public int x, y; 

Public Point (int x, int y) {
this.x=x; 
this.y=y; 
} 

Public Point (Point a) {
This. X=a.x; 
This. Y=a.y; 
} 
} 

//can't use recursive maze problem BFS 
//the grid 0 to 1 obstacle 
//@ return the return value is the pre on behalf of each point of the previous point 
Static int aa, bb, 
Static int [] [] dis=new int [] [] {{1, 0}, {1, 0}, {0, 1}, {0, 1}}; 

The static Point [] [] map (int [] [] the grid) {
Queue Q=new LinkedList<> (a); 
Q.o ffer (new Point (0, 0)); 
Int n=grid. Length, m=grid [0]. Length; 
Point [] [] pre=new Point [n] [m]. 
Boolean [] [] vis=new Boolean [n] [m]. 
While (! Q.i sEmpty ()) {
Point p=q.p oll (); 
Vis [p.x] [p.y]=true; 
If (p.x==n - 1 & amp; & P.y==m - 1) 
Return the pre. 
for (int i=0; I & lt; 4. I++) {
Int nx=p.x + dis [I] [0], ny=p.y + dis [I] [1]; 
If (nx & gt;=0 & amp; & Nx & lt; N & amp; & Ny & gt;=0 & amp; & Ny & lt; M & amp; & ! Vis/nx/ny & amp; & The grid (nx) [New York]==0) {
The pre [nx] [ny]=new Point (p.x, p.y); 
Q.o ffer (new Point (nx, ny)); 
} 
} 
} 
Return new Point [0] [0]; 
} 

 

Case '3' : 
Aa, bb, int 
System. The out. Println (" please enter the maze of lines: "); 
Int p=sc. NextInt (); 
System. The out. Println (" please enter the column number of the maze: "); 
Int q=sc. NextInt (); 
Sc. NextLine (); 
Int [] [] grid=new int [p] [q]; 
String row; 
for(int i=0; I & lt; p; I++) {
System. The out. Println (" please enter the maze of the first "+ (I + 1) +" row (0 representatives can walk, 1 representative can't walk, separated by a space) : "); 
The row=sc. NextLine (); 
String [] y=row. The split (" "); 
for(int j=0; J & lt; q; J++) {
The grid [I] [j]=Integer. ParseInt (y) [j]. 
} 
} 
Point [] [] pre=map (grid); 
If (Objects. RequireNonNull (pre) [1] p/q - 1==null) {
System. The out. Println (" no exports of labyrinth "); 
} else {
The grid [p - 1]] [q - 1=2; 
Aa=pre [p - 1] [q - 1]. X. 
Bb=pre [p - 1] [q - 1] y; 
While (true) {
The grid/aa/bb=2; 
Aa=pre/aa/bb. X; 
Bb=pre/aa/bb] y; 
If (==0 aa & amp; & Bb==0) {
The grid/aa/bb=2; 
break; 
} 
} 
System. The out. Println (grid); 
} 
break; 

Is the idea of the bb=pre/aa/bb. Y; This line of Exception in the thread "is the main" Java. Lang. NullPointerException

CodePudding user response:

With the debug code can solve the problem, why must turn to the Internet?