The expression i // 3 * 3 + j // 3 calculates the box index for a 9x9 Sudoku board, where:

• i is the row number (0 to 8).

• j is the column number (0 to 8).

Here's how it works step by step:

1. i // 3: This divides the row number by 3 and takes the in...

Shubham gives a good step by step explanation, but my brain wanted a conceptual answer to remember this pattern. I would describe it this way:

We use integer division to map/reduce each row and column multiple of three to the same number so they all point to the same ...