Spiral matrix

data_structures/arrays/spiral_matrix.py

@@ -0,0 +1,64 @@
+class Solution:
+ def generate_matrix(self, n: int) -> list[list[int]]:
+ # create an n x n matrix filled with zeros
+ result = [[0] * n for _ in range(n)]
+
+ # Start filling numbers from 1 to n^2
+ value = 1
+
+ # Define the boundaries for rows and columns
+ rowStart, rowEnd = 0, n - 1
+ colStart, colEnd = 0, n - 1
+
+ # Continue filling the matrix layer by layer in spiral order
+ while rowStart <= rowEnd and colStart <= colEnd:
+
+ # Step 1: Fill the top row (left → right)
+ for i in range(colStart, colEnd + 1):
+ result[rowStart][i] = value # assign the current value
+ value += 1 # move to next number
+ rowStart += 1 # move top boundary down (row filled)
+
+ # Step 2: Fill the rightmost column (top → bottom)
+ for j in range(rowStart, rowEnd + 1):
+ result[j][colEnd] = value
+ value += 1
+ colEnd -= 1 # move right boundary left (column filled)
+
+ # Step 3: Fill the bottom row (right → left)
+ # Only if there are rows remaining to fill
+ if rowStart <= rowEnd:
+ for k in range(colEnd, colStart - 1, -1):
+ result[rowEnd][k] = value
+ value += 1
+ rowEnd -= 1 # move bottom boundary up (row filled)
+
+ # Step 4: Fill the leftmost column (bottom → top)
+ # Only if there are columns remaining to fill
+ if colStart <= colEnd:
+ for l in range(rowEnd, rowStart - 1, -1):
+ result[l][colStart] = value
+ value += 1
+ col_start += 1
+
+ # return the completed spiral matrix
+ return result
+
+
+# example usage
+solution = Solution()
+n = 3 # change this to any number, e.g., 4 or 5
+matrix = solution.generate_matrix(n)
+
+# print the spiral matrix row by row
+for row in matrix:
+ print(row)
+
+
+# Output: 
+'''
+ [1, 2, 3]
+ [8, 9, 4]
+ [7, 6, 5]
+
+'''