CodeHS 8.1.5 requires updating the final elements of three 2D array rows, replacing placeholder zeros with specific values calculated using a helper method, including the first row's length, the total element count, and sum of specific elements. Implementation involves iterating through rows to sum lengths and using the arr[row][col] = value formula to update indices, taking care to avoid out-of-bounds errors. For code examples and further explanation, see the solutions on Reddit.
| Mistake | Solution |
|---------|----------|
| Using matrix.length for columns | Use matrix[0].length for columns (if rectangular) |
| Forgetting rows can have different lengths (jagged arrays) | Always check matrix[i].length in inner loop |
| Modifying original array when you shouldn't | Copy the array first: let copy = matrix.map(row => [...row]); |
| Off-by-one errors in loops | Use < matrix.length, not <= |
| Trying to access index out of bounds | Ensure row and col are valid before using | Codehs 8.1.5 Manipulating 2d Arrays
In Java (the language typically used on CodeHS), you can visualize a 2D array like this: CodeHS 8
Then came the test.
) to replace the incorrect placeholder values with specific calculated totals: : Change the last element to the length of the first array : Change the last element to the total number of elements in the entire 2D array. : Change the last element to the sum of the first value and the second-to-last value in that specific array. Key Logic for the Task Counting Total Elements Common Mistakes & Debugging Tips | Mistake |
array[row].length gives you the number of columns in that specific row. 3. Conditional Logic (If-Statements)