Two-Dimensional Arrays

By the end, you can

• Explain what a 2D array is and how it relates to an array of arrays.
• Access any cell using `grid[row][col]` and explain why row comes first.
• Distinguish rectangular grids from jagged arrays and know when `grid[0].length` is unreliable.
• Measure a grid's dimensions using `grid.length` and `grid[0].length`.
• Create a grid safely with `Array.from` and explain why `Array(n).fill(array)` is a bug.
• Write nested loops to traverse every cell and state the time complexity.
• Compute the flat row-major memory offset for any `[row][col]` coordinate.
• Implement search, row-sum, and column-sum operations on a 2D array.
• Identify and avoid the out-of-bounds error by using correct loop bounds.