Maze solver with DFS

Question

I am trying to solve the maze using DFS algorithm.ORDER: West- North-South-East My output works in this logic Labyrinth picture1. It should not go up after the point (3,3),because the order of priority is west. What should I do?

#include <stdio.h>

char matrix[8][8];

void File()
{
        int i,j;
  

    FILE *file1;
    file1=fopen("maze1.txt","r");
 
    for(i=0; i<8; i++){
        for(j=0;j<8;j++)
        {
        fscanf (file1, " %c", &matrix[i][j]);
        
        printf("%c ",matrix[i][j]);
       }
    printf("\n");
    }
}
void Print()
{
    int i,j;
    for(i=0;i<8;i++)
    {
        for(j=0;j<8;j++)
        {
            printf("%c ",matrix[i][j]);
            }
    printf("\n");       
    }
}
void stepDFS()
{
    int i,j;
    for(i=0;i<8;i++)
    {
        for(j=0;j<8;j++)
        {
            if(matrix[i][j] == 's')
            {
                
                    DFS(i,j);
                        
               
            
            }
            
        }
    printf("\n");       
    }
    
}
 DFS(int i,int j)
{
    if(matrix[i][j-1] == '-')
    {
        matrix[i][j-1] = '.';
        DFS(i,j-1);
    }
     if(matrix[i-1][j] == '-')
    {
        matrix[i-1][j] = '.';
        DFS(i-1,j);
    }
     if(matrix[i+1][j] == '-')
    {
        matrix[i+1][j] = '.';
        DFS(i+1,j);

    }
     if(matrix[i][j+1] == '-')
    {
        matrix[i][j+1] = '.';
       DFS(i,j+1);

    }
    
    
}
int main()
{
    File();
    Print();
    stepDFS();
    Print();
    return 0;
}

maze1.txt ( # wall - null . step)

# # # # # # # #  
# g - - # - - #       
# # # - - - # # 
# - # # - - - # 
# - - # - - - #
# - - - - # # # 
# - - # - - s #
# # # # # # # #

output

# # # # # # # #
# g . . # . . #
# # # . . . # #
# . # # . . . #
# . . # . . . #
# . . . . # # #
# . . # . . s #
# # # # # # # #

I don't know if this should be the output

# # # # # # # #  
# g . . # - - #       
# # # . . - # # 
# . # # . - - # 
# . . # . - - #
# . . . . # # # 
# - - # . . s #
# # # # # # # #

--------------UPDATE-------------- STEP BY STEP

#include <stdio.h>

char matrix[8][8];

void ReadFile()
{
    printf("\n\n\n                START MAZE    ");
    int x,y;
    FILE *file1;
    file1=fopen("myMaze.txt","r");
 
    for(x=0; x<8; x++){
        for(y=0;y<8;y++)
        {
        fscanf (file1, " %c", &matrix[x][y]);
        
      
       }
    printf("\n");
    }
}



void PrintMaze()
{ 
    int x,y;
    for(x=0;x<8;x++)
    {
        printf("                ");
        for(y=0;y<8;y++)
        {
             
            printf(" %c ",matrix[x][y]);
        }
     
    printf("\n");       
    }
    printf("\n\n\n\n");
}
  
  
int DFS(int x,int y){
 

 
    if(matrix[x][y]=='g') // goal
    {
        return 1;
    }
      if(matrix[x][y-1] == '-' ){ //WEST
           

        
        matrix[x][y-1] = '.';
        PrintMaze();
        
        
        if(DFS(x,y-1)){
            
            matrix[x][y-1] ='.'; 
            PrintMaze();
            
            return 1;
        }
        else{
            DFS(x,y-1);
            return 0;
        
         }
         DFS(x,y-1);
      

     }
      if(matrix[x-1][y] == '-'){  //NORTH
       
   
        matrix[x-1][y] = '.';
        PrintMaze();
        
        if(DFS(x-1,y)){
            
            matrix[x-1][y] = '.';
            PrintMaze();
            
            return 1;
        }
        else{
            DFS(x-1,y);
            return 0;
        }
     
         DFS(x-1,y);
    

     }
    
    
 
    
    
    
       if(matrix[x+1][y] == '-'){ //SOUTH
             
     
        matrix[x+1][y] = '.';
        PrintMaze();
        
        if(DFS(x+1,y)){
            
           matrix[x+1][y] ='.'; 
           PrintMaze();
            
            return 1;
            
        }
        else{
          DFS(x+1,y);
            return 0;
        }
        
        DFS(x+1,y);
 
    }  
  
    
           if(matrix[x][y+1] == '-'){     //EAST
          

        matrix[x][y+1] = '.';
       
        if(DFS(x,y+1)){
            
        matrix[x][y+1] = '.'; 
        PrintMaze();
          
            return 1;
        }
        else{
            DFS(x,y+1);
            return 0;
        }
        
        DFS(x,y+1);
    
    }
    
 

    return 0;


}


void StartSearch()
{ 
    printf("                  STEP BY STEP");

    int x,y;

 
    for(x=0;x<8;x++)
    {
        for(y=0;y<8;y++)
        {
            if(matrix[x][y] == 's')//start
            {
              DFS(x,y);
 
             }
        }
        
    printf("\n");  
         
    }
 
}
 
int main()
{
    ReadFile();
    
    PrintMaze();
    
    StartSearch();
    
    PrintMaze();
    
    return 0;
}

myMaze.txt

# # # # # # # #  
# g - - # - - #       
# # # - - - # # 
# - # # - - - # 
# - - # - - - #
# - - - - # # # 
# - - # - - s #
# # # # # # # #

DFS determines direction based on first if condition inside the function.Other directions should also be considered.

You should add some termination code (stop all when `g` is reached`) — Mathieu, May 04 '22 at 13:57
This is a follow up to https://stackoverflow.com/q/72072024/589924 — ikegami, May 04 '22 at 14:04
I am with Mathieu. I think your code DOES go west first, finds the goal and then still does the other directions. You can see that everything has been stepped in. Also, just do a print after time you write a "." anywhere and watch the "movie". — Yunnosch, May 04 '22 at 14:04
while(matrix[i][j] != 'g') {if(matrix[i][j] == 'g') break;} is it correct to add this to the DFS function? — OceanWaves, May 04 '22 at 14:05
You'd have to show the changed code to show what you mean by that. Try, test, think. Watch the movie. — Yunnosch, May 04 '22 at 14:06
@OceanWaves No, since you go to a case only if it contains a ``'` `, you should test for `g` in all directions. — Mathieu, May 04 '22 at 14:06
@OceanWaves should should read https://stackoverflow.com/a/72072154/1212012 more carefully: having a return value from `DFS` is important — Mathieu, May 04 '22 at 14:08
while(matrix[i][j] != 'g') {if(matrix[i][j] == 'g') break;} I tried this it goes into an endless loop — OceanWaves, May 04 '22 at 14:08
Should I create a separate check function for the return value? — OceanWaves, May 04 '22 at 14:11
First have a return value for DFS(), indicating whether it found the goal. It currently does not even specify `void`you know... Then use it to only try more directions if the currently tried one did not find it. — Yunnosch, May 04 '22 at 14:18

ikegami · Accepted Answer · 2022-05-17T14:06:12.167

5

First of all, enable and heed your compiler's warnings! (With gcc, I use -Wall -Wextra -pedantic). You were told to this already. Why come to SO when the compiler can answer your questions for you!

DFS(int i,int j) means int DFS(int i,int j), but you meant to use void DFS(int i,int j). (It's not what you need, though. You already had what you need.)

Next, let's identify the expected output since you're not sure. This maze has five solutions (ignoring solutions that pointlessly visit a cell twice).

Length = 9
# # # # # # # #
# g . . # - - #
# # # . . - # #
# - # # . - - #
# - - # . - - #
# - - - . # # #
# - - # . . s #
# # # # # # # #

Length = 11
# # # # # # # #        # # # # # # # #
# g . . # - - #        # g . . # - - #
# # # . . - # #        # # # . . . # #
# - # # . . - #        # - # # - . - #
# - - # . . - #        # - - # . . - #
# - - - . # # #        # - - - . # # #
# - - # . . s #        # - - # . . s #
# # # # # # # #        # # # # # # # #

Length = 13
# # # # # # # #        # # # # # # # #
# g . . # - - #        # g . . # - - #
# # # . . - # #        # # # . . . # #
# - # # . . . #        # - # # - . . #
# - - # . . . #        # - - # . . . #
# - - - . # # #        # - - - . # # #
# - - # . . s #        # - - # . . s #
# # # # # # # #        # # # # # # # #

Any of these would be a valid output. Obviously, the first path is shorter than the other two, but a DFS doesn't (necessarily) find the shortest path. (You'd want a BFS for that.)

On to the question.

You have two problems:

You are marking every cell you've visited, whether it's part of the path or not.
You never stop searching, so you end up visiting every reachable cell.

In order to solve the two problems, one important change needs to be made. DFS needs to return whether the cell identified by its parameters is part of the path or not.

DFS should return 1 if the cell is part of the path, or 0 if it isn't.

So how do you know if the cell is part of the path?

If the current cell is g, the current cell is part of the path.
If the cell to the North is part of the path (i.e. if DFS(y-1,x) returned a true value), the current cell is part of the path.
If the cell to the South is part of the path (i.e. if DFS(y+1,x) returned a true value), the current cell is part of the path.
If the cell to the West is part of the path (i.e. if DFS(y,x-1) returned a true value), the current cell is part of the path.
If the cell to the East is part of the path (i.e. if DFS(y,x+1) returned a true value), the current cell is part of the path.
Otherwise, the cell is not part of the path.

Problem #2: You keep searching after finding a solution.

As soon as you know a cell is part of the path, DFS should return. Immediately. Don't go on checking the node to the South if the cell to the North is part of the path!

Problem #1: You are marking every cell you've visited

When you enter DFS, you mark the cell as being part of the path by making it .. This is good as it prevents infinite loop.

But it might not end up being part of the path. As previously mentioned, you need to restore its value to - if it turns out not to be part of the path.

edited May 17 '22 at 14:06

answered May 04 '22 at 14:23

ikegami

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Rewrote most of answer – ikegami May 04 '22 at 15:02
I made changes in DFS @ikegami – OceanWaves May 04 '22 at 16:59
1

How about you to the changes I mentioned instead? (Rolled back the changes to the question. Don't invalidate answers by removing the problems you're asking about from the question!) – ikegami May 04 '22 at 20:00
Yes, I am trying to implement what you said.return 1 part of road return 0 not part of road i tried this way.@ikegami – OceanWaves May 04 '22 at 20:21
1

You returned `1`, but not just when it was part of the path. I've described in detail when that is – ikegami May 04 '22 at 21:16
I'm trying to understand . Do I need to use a linked list structure in the codes?@ikegami – OceanWaves May 05 '22 at 15:06
1

Nope. `matrix` keeps track of the progress (by switching `-` to `.`). – ikegami May 05 '22 at 15:55
How can I specify the order of priority when coding? West-North-South-East.@ikegami – OceanWaves May 10 '22 at 12:52
Because he doesn't know in which order to go. It traverses the entire matrix – OceanWaves May 10 '22 at 12:58
1

The order doesn't matter. – ikegami May 10 '22 at 13:01
Hello ikegami please, help me. How do i know if it returns true value ? Because all (-) are elements of the matrix.@ikegami – OceanWaves May 17 '22 at 09:29
1

An if statement can be used to check if something is true or false. – ikegami May 17 '22 at 14:01
Thank you so much for answering my questions.I added an updated code am I on the right track? @ikegami – OceanWaves May 17 '22 at 17:59
No, quite the opposite. You still don't check the value returned by DFS. DFS always returns 0. Why do you ask for help, then ignore it to do something completely different? – ikegami May 17 '22 at 19:49
I'm just trying to follow your description. – OceanWaves May 17 '22 at 20:38
Really? Where's the return `return 1` in DFS? And where to do you check the value returned by DFS? These are the two things I said you needed. I literally spelled out the changes you needed, and they weren't made. – ikegami May 17 '22 at 20:52
I used the nested if structure for checking. After the dead end, there's no turning back.how can i fix that part ? I updated the question. – OceanWaves May 18 '22 at 11:45
Algorithm should also work correctly on different maze text files. – OceanWaves May 18 '22 at 11:52
Why are you returning 1 for a dead end? – ikegami May 18 '22 at 13:42
I replaced the else statements with return 0 but it didn't fix. – OceanWaves May 18 '22 at 14:05
Please fix your indentation. Your code is absolutely unreadable. – ikegami May 18 '22 at 14:31
You only ever try to go in one direction. Not always the same direction. But as soon as you try one direction, you exit the sub. – ikegami May 18 '22 at 14:37
How can the maze go to other directions ? – OceanWaves May 18 '22 at 18:37
(5,3) ->>> (5,2) and (4,3) (5,2) : DEAD END (4,3) : GOAL – OceanWaves May 18 '22 at 18:43
Is there any way to solve this problem?@ikegami – OceanWaves May 19 '22 at 16:41
My answer says how to do it in great detail. – ikegami May 19 '22 at 18:00
yes,I used do while but nothing changed. – OceanWaves May 19 '22 at 19:27
I checked it in step by step. It finding the goal but not stopping.@ikegami – OceanWaves May 21 '22 at 12:54

Maze solver with DFS

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