Write a recursive function diag2list_rec(grid), where grid is an n n square list of lists, that returns a list consisting of the diagonal elements of grid, i.e., the elements grid[0][0], grid[1][1], ..., grid[n1][n1].

You can assume that grid is a square list of lists, i.e., you don't have to check for this.

You must use a helper function useful for this problem.

Programming Requirements

Solve this problem using recursion. You are allowed to use onlythe following programming constructs:

if statements;

return statements;

assignment;

recursive function calls (if you use any helper functions then these must all be recursive as well);

comparison operations (==, !=, etc.);

list indexing and slicing;

list concatenation/extension.

Solutions that go outside these constructs, e.g., by using for/while loops or list comprehensions, will not get credit.