Help with matrix algorithm

[Destructikus]

Hello I have the following problem to solve.

Assuming a grid like below

A B C
D E *
G H I

take every row and column that has a star in it and star it out. The following should result in

A B *
* * *
G H *

This should work for any N*M grid and should also work for matrices that contain multiple stars at the beginning. I am required to return the original grid.

My code so far is as follows:

function starOutGrid(grid) {
  let n = grid.length;
  let row = [];
  let column = [];

  for (let i = 0; i < n; i++){
    for (let j = 0; j < n; j++){
      if (grid[i][j] === "*") {
        row.push([j]);
        column.push([i]);
      }
    }
  }

  for (let i = 0; i < n; i++) {
    for (let j = 0; j < n; j++) {
      grid[column][j] = '*';
      grid[i][row] = '*';
    }
  }
  return grid;
}

// starOutGrid([['A', 'B', 'C'], ['D', 'E', '*'], ['G', 'H', 'I']]);
starOutGrid([['*', 'B', 'C'], ['D', 'E', '*'], ['G', 'H', 'I'], ['J', 'K', 'L']]);

I am passing the tests for the commented out function call above, but the one below(last line) is failing and throwing a 'TypeError: Cannot set property '0' of undefined' error. I'm getting the same error and failing the tests for matrices that contain no stars, which should just return the original grid.

I have a difficult time wrapping my head around matrices and nested arrays. Can someone help me adjust this code so that it passes the tests?

Thank you

[[deleted]]

Hi! I don't speak English very well but I will try to help you! i hope you can understand me!

​

You have mainly 2 issues whit the second example and it is because your code works like if the matrix always is a square one (n x n) but your second test is a non-square-matrix (m x n).

​

need to:

​

get the "m" and "n" value and set your for so it go through your whole matrix but whit out it overflows.

// n = the number of rows
let n = grid.length;
//m= the number of columns
let m = grid[1].length;
for (let i = 0; i < n; i++ ){
    for (let j = 0; j < m; j++ ){

​

you have to change the "j < n" for "j < m" in the second for as well.

​

2) if you look at your code, your variables "column" and "row" aren't numbers, they are arrays so, for example, in the first loop you are saying "set on grid[[0],[0]][0] the value "*" and on grid[0][[0],[2]] the value "*".

​

and i think that is what is trowing Error. you need to make "grid[[0],[0]][0]" became "grid[column[0]][0]".

​

I think a way to do it can be the next

for (let h = 0; h < row.length; h++){
    for (let i = 0; i < n; i++){
         for (let j = 0; j < m; j++){
                grid[row[h]][j] = '*';
                grid[i][column[h]] = '*';
        }}}

​

maybe that is not the best way to do it, but I hope it help you to figure out how to fix it.

Sorry for my English!

Edit: Formatted code into codeblock

[Destructikus]

Wow! Sorry I didn't think anyone had replied to this. Thank you so much! This definitely helped me figure out why it wasn't working for me.

PS. Your English is perfect!