Spiral Matrix
Return all elements of a matrix in spiral order.
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Lesson notes
Try it before you watch
Restate the problem in your own words, list the edge cases, and sketch a solution with its running time. Then play the video and compare.
Reveal the key idea
Keep four boundaries (top, bottom, left, right). Walk the top row, right column, bottom row and left column, shrinking the matching boundary after each pass.
Pattern: Matrices & grids. Keep row and column boundaries explicit and treat grid cells as graph nodes when needed.
Complexity
| Measure | Bound |
|---|---|
| Time | O(m · n) |
| Extra space | O(1) extra |
Walkthroughs often start from a simpler approach first; aim to reach these bounds. New to Big-O? Read understanding algorithmic complexity.