Spiral Matrix

Problem

https://leetcode.com/problems/spiral-matrix/

Given an m x n matrix, return all elements of the matrix in spiral order.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [1,2,3,6,9,8,7,4,5]

Example 2:

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]

Constraints:

• m == matrix.length

• n == matrix[i].length

• 1 <= m, n <= 10

• -100 <= matrix[i][j] <= 100

Pattern

Array, Matrix

Approaches

Simulation

Code

def spiralOrder(matrix: list[list[int]]) -> list[int]:
    """Return all elements of *matrix* in spiral order."""
    m = len(matrix)
    n = len(matrix[0])

    directions = [
        (0, 1),
        (1, 0),
        (0, -1),
        (-1, 0),
    ]

    i = 0
    j = 0
    d = 0

    output: list[int] = []

    left = 0
    right = n - 1
    top = 1
    bottom = m - 1

    while len(output) < m * n:
        output.append(matrix[i][j])

        hit_right = d == 0 and j == right
        hit_bottom = d == 1 and i == bottom
        hit_left = d == 2 and j == left
        hit_top = d == 3 and i == top

        if hit_right:
            d += 1
            right -= 1
        if hit_bottom:
            d += 1
            bottom -= 1
        if hit_left:
            d += 1
            left += 1
        if hit_top:
            d = (d + 1) % 4
            top += 1

        i += directions[d][0]
        j += directions[d][1]

    return output

Test

>>> from spiral_matrix__simulation import spiralOrder
>>> spiralOrder([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
[1, 2, 3, 6, 9, 8, 7, 4, 5]
>>> spiralOrder([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]])
[1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7]

spiral_matrix__simulation.spiralOrder(matrix: list[list[int]]) → list[int]

Return all elements of matrix in spiral order.