Insert New Row

Take a 2D list and insert a new row at a given position.

lists insert rows 2d

Write a function `insert_row(matrix, row, index)` in Python that takes a list of lists (representing a matrix), a new row (a list), and an integer index, and returns a new matrix with the new row inserted at the given index. The insertion follows the same rules as `list.insert`:

- If `index` is non-negative, the row is inserted so that it appears before the row currently at that index (indexing from 0).
- If `index` is negative, it counts from the end (e.g., -1 inserts before the last row).
- Any index beyond the bounds will insert at the beginning or end respectively, consistent with Python's `list.insert` behavior.

The original matrix and row should remain unchanged; the function must return a new matrix (shallow copy of rows is acceptable).

Constraints

`matrix` is a list of lists, possibly empty. The row is a list (may be empty). The index is an integer. Time complexity: O(n) as list insertion, space O(1) for references (not counting output).

Example

```python
>>> insert_row([[1,2],[3,4]], [9,9], 1)
[[1,2],[9,9],[3,4]]
>>> insert_row([], [5,6], 0)
[[5,6]]
>>> insert_row([[1,2],[3,4]], [7,8], -1)
[[1,2],[7,8],[3,4]]
>>> insert_row([[1,2],[3,4]], [0], 10)
[[1,2],[3,4],[0]]
```

5 points ~5 min

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Hints

Make a copy of the matrix using `matrix.copy()` or `list(matrix)` to avoid modifying the original.

Use the list `.insert(index, row)` method on the copied list.

Remember that this should work for empty matrices and out-of-range indices.

Think about how Python's list.insert handles negative indices—you don't need to do anything special.

Test Results

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