DAY 64 OF 90 · Walk the grid

Diagonal

Medium90 Days of Looping

Inputs

cells is a square grid: n rows of n whole numbers each (n from 1 to 5), from -9 to 9.

Your tasks

Create a number total that starts at 0.
Use a single loop for i from 0 up to n - 1. Add cells[i][i] (the main diagonal) and cells[i][n - 1 - i] (the other diagonal) to total.
A cell on both diagonals, the middle of an odd-sized grid, must only be counted once.
Complete diagonalTotal so it returns total. Return it, do not print it.

Example

With cells = [[1, 2, 3], [4, 5, 6], [7, 8, 9]], diagonalTotal returns 25.

Rules

In a 1 by 1 grid, the single cell is counted once.

Test data

TEST DATA 1: cells is [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

TEST DATA 2: cells is [[5]]

Practice focus

Two-dimensional data is a loop over rows with a loop over columns inside. Grids lead straight to flood fill, islands, dynamic programming tables and path problems.

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