Spiral Matrix

Medium · Math & Geometry

You are given a 2D grid of integers with r rows and c columns. Return the elements of the grid as a single list ordered by walking the outer boundary clockwise starting at the top-left corner, then continuing inward layer by layer in the same clockwise spiral pattern until every cell has been visited exactly once.

Examples

Input:  matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [1,2,3,6,9,8,7,4,5]
Why:    Walking the outer ring clockwise then spiraling inward visits the center last.

Input:  matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]
Why:    The top row, right column, bottom row, and left column are traced in order, then the remaining inner row is read left to right.

Input:  matrix = [[7]]
Output: [7]
Why:    A single cell matrix has only one element to visit.

Constraints

1 <= matrix.length, matrix[0].length <= 10, -100 <= matrix[i][j] <= 100

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Practise Spiral Matrix

This statement is written for CodeSpeek. The problem is part of the NeetCode 150 list; Watch NeetCode's explanation of Spiral Matrix. Reference solutions from the NeetCode repository (MIT) are used to verify our tests.