Create spiral_merge_array_traversal.py

data_structures/arrays/spiral_merge_array_traversal.py

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+from typing import List
+
+
+def spiral_traverse(matrix: List[List[int]]) -> List[int]:
+    """
+    Takes a 2D array (matrix) and returns its elements in spiral order (clockwise from the top-left).
+
+    Uses four pointers: top, bottom, left, right to track the current layer of the matrix.
+    Loops through top row → right column → bottom row → left column until all elements are visited.
+    """
+    result = []
+    if not matrix:
+        return result
+
+    top, bottom = 0, len(matrix) - 1
+    left, right = 0, len(matrix[0]) - 1
+
+    while top <= bottom and left <= right:
+        # Traverse top row from left to right
+        for j in range(left, right + 1):
+            result.append(matrix[top][j])
+        top += 1  # move top boundary down
+
+        # Traverse right column from top to bottom
+        for i in range(top, bottom + 1):
+            result.append(matrix[i][right])
+        right -= 1  # move right boundary left
+
+        if top <= bottom:
+            # Traverse bottom row from right to left
+            for j in range(right, left - 1, -1):
+                result.append(matrix[bottom][j])
+            bottom -= 1  # move bottom boundary up
+
+        if left <= right:
+            # Traverse left column from bottom to top
+            for i in range(bottom, top - 1, -1):
+                result.append(matrix[i][left])
+            left += 1  # move left boundary right
+
+    return result
+
+
+def spiral_merge_matrices(matrices: List[List[List[int]]]) -> List[int]:
+    """
+    Accepts a list of matrices.
+
+    First, converts each matrix into its spiral order list using spiral_traverse.
+    Then merges them alternately: take the first element from each spiral, then the second, etc., until all are merged.
+    """
+    merged = []
+    # Convert each matrix to spiral order
+    spirals = [spiral_traverse(m) for m in matrices]
+    max_len = max(len(s) for s in spirals)
+
+    # Merge elements alternately from each spiral
+    for i in range(max_len):
+        for s in spirals:
+            if i < len(s):
+                merged.append(s[i])
+    return merged
+
+
+if __name__ == "__main__":
+    """
+    Ensures that the example usage code runs only if the script is executed directly,
+    not when imported as a module.
+
+    Example Output for the given mat1 and mat2:
+    Merged Spiral Array: [1, 10, 2, 11, 3, 12, 6, 15, 9, 18, 8, 17, 7, 16, 4, 13, 5, 14]
+    """
+    mat1 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
+
+    mat2 = [[10, 11, 12], [13, 14, 15], [16, 17, 18]]
+
+    merged = spiral_merge_matrices([mat1, mat2])
+    print("Merged Spiral Array:", merged)