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Recursive function Help

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Taylor
Taylor il 17 Nov 2011
I have code here with a maze that uses a recursive function to solve the maze and then prints out all the coordinates from start to exit.
% clear workspace
clearvars;
clear global MAZE ROWLIMIT COLLIMIT ROWEND COLEND
% maze, its size, and endpoint must be global
global MAZE ROWLIMIT COLLIMIT ROWEND COLEND
% maze
MAZE(1,:) = '############';
MAZE(2,:) = '# # #';
MAZE(3,:) = ' # # #### #';
MAZE(4,:) = '### # # #';
MAZE(5,:) = '# ### # ';
MAZE(6,:) = '#### # # # #';
MAZE(7,:) = '# # # # # #';
MAZE(8,:) = '## # # # # #';
MAZE(9,:) = '# # #';
MAZE(10,:) = '###### ### #';
MAZE(11,:) = '# # #';
MAZE(12,:) = '############';
% constants & initial values
ROWLIMIT = 12;
COLLIMIT = 12;
rowbegin = 3;
colbegin = 1;
ROWEND = 5;
COLEND = 12;
% solve the maze -- (0,0) is a dummy "previous" value
isPathToExit(0, 0, rowbegin, colbegin);
This is the code I written so far for the recursive function 'isPathToExit':
function success = isPathToExit(previous_row, previous_col, current_row, current_col)
% Finds a path from entrance to exit through the maze
% base case
global MAZE ROWLIMIT COLLIMIT ROWEND COLEND
if current_row == ROWEND && current_col == COLEND
disp(sprintf('(%i, %i)', current_row, current_col));
success = true;
return;
else
success = false;
end
% recursion
if current_row+1 ~= previous_row && MAZE(current_row+1, current_col) ~= '#' && current_row+1 ~= ROWLIMIT && current_row ~= 0
success = isPathToExit(current_row, current_col, current_row+1, current_col);
if success
disp(sprintf('(%i, %i)', current_row+1, current_col));
return;
end
end
if current_row-1 ~= previous_row && MAZE(current_row-1, current_col) ~= '#' && current_row-1 ~= ROWLIMIT && current_row ~= 0
success = isPathToExit(current_row, current_col, current_row-1, current_col);
if success
disp(sprintf('(%i, %i)', current_row-1, current_col));
return;
end
end
if current_col+1 ~= previous_col && MAZE(current_row, current_col+1) ~= '#' && current_col+1 ~= COLLIMIT && current_col ~= 0
success = isPathToExit(current_row, current_col, current_row, current_col+1);
if success
disp(sprintf('(%i, %i)', current_row, current_col+1));
return;
end
end
if current_col-1 ~= previous_col && MAZE(current_row, current_col-1) ~= '#' && current_col-1 ~= COLLIMIT && current_col ~= 0
success = isPathToExit(current_row, current_col, current_row, current_col+1);
if success
disp(sprintf('(%i, %i)', current_row, current_col-1));
return;
end
end
When I run it, it displays the points up to a wall of the maze and stops. I need it display the points from start to exit.

Risposta accettata

Alex
Alex il 17 Nov 2011
A few comments: 1. using global variables, then settings and clearing them is a bad habit to get into.
2. disp(Maze(i,j)); will not show the coordinates, it'll only show the element of the Maze that is the current position, which all of those should be " " white space.
If you want the indicies, use:
disp(sprintf('The current maze index is %i and %i, current_row, current_col));
3. Your if statements are very hard to read. Also, you're putting the recursive statements within the if statement itself, I would recommend separating those. This makes debugging easier. Additionally, you don't need to have all those conditions based on row_limit, col_limit, and such. Since the entire maze is surounded by '#', all you need to do is check in the 3 remaining directions for a solution
ex:
function success = Recursive_Fcn(prev_row, prev_col, next_row, next_col)
if (at maze exit)
sucess = true
return
else
sucess = false;
end
if(prev pt was not from up && up point is clear && ~sucess )
sucess = recursive statement(up direction)
if(success)
print pt
end
end
if(prev pt was not from down && down point is clear && ~sucess )
sucess = recursive statement(down direction)
if(success)
print pt
end
end
if(prev pt was not from lwft && left point is clear && ~sucess )
sucess = recursive statement(left direction)
if(success)
print pt
end
end
if(prev pt not from right && right pt is clear && ~success)
success = recursive statement(right direction)
if(success)
print pt
end
end
return
I made these changes to your code and got it to work.
  31 Commenti
Taylor
Taylor il 21 Nov 2011
I figured it out. I had to switch the last two conditions for each direction.
Now I get the correct output. Finally.
Thanks for the help.
Alex
Alex il 21 Nov 2011
+ the answer please.

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