moving through variables in matrix with recursion

Question

I'm trying to write a function which got a kind of a matrix - a list that consists of sub-lists So I want to go through all the matrix members and print them out. Only in recursion! But I dont know how to create a good "stop conditions" for my function. So I get more numbers than I wanted.

def mission(mat):    

def move(mat, i=0, j=0 ,k=0):
    print(mat[i][j])
    if j<(len(mat[0])-1):
        move(mat,i,j+1)
    if i<(len(mat)-1):
        move(mat,i+1,0)
    
    

move(mat)


mat = [[1, 0, 0, 3, 0],
[0, 0, 2, 3, 0],
[2, 0, 0, 2, 0],
[0, 1, 2, 3, 3]]        
mission(mat)

*edit I got another question - is there a way to decrease 2 list that looks like the mat function i did here (with the same length - just different numbers) without using numpy or for ?

Answer 1

You can test for end condition on function start, and check if you have already crossed the last item in the last sublist. If so, you return.

if(i == len(mat) - 1 and j == len(mat[0]) - 1):
    return

Then, you check whether you are at the last item in your current sublist, and if so, increment the sublist index i and set the item index back to 0.

if(j == len(mat[0]) - 1):
    i += 1
    j = 0

If you are neither at the end of the whole 2d matrix (list), nor the end of any sublist, you just need to increment the item index j.

else:
    j += 1

Then, you can safely call your function recursively. The whole code ends up looking like this.

def move(mat, i=0, j=0):
    print(mat[i][j])
    if(i == len(mat) - 1 and j == len(mat[0]) - 1):
        return
    if(j == len(mat[0]) - 1):
        i += 1
        j = 0
    else:
        j += 1

    move(mat, i, j)


mat = [[1, 0, 0, 3, 0],
       [0, 0, 2, 3, 0],
       [2, 0, 0, 2, 0],
       [0, 1, 2, 3, 3]]

move(mat)

Output::

1
0
0
3
0
0
0
2
3
0
2
0
0
2
0
0
1
2
3
3

Answer 2

as for the move function, simply change the 2nd if to elif

def move(mat, i=0, j=0):
    print(mat[i][j])
    if j<(len(mat[0])-1):
        move(mat,i,j+1)
    elif i<(len(mat)-1):
        move(mat,i+1,0)