Boundary Traversal of a matrix

Approach

• It can be done with naive approach which will take O(n^m)

• iterate through all elements

• Check if an element is on boundary or not

  i == 0 || j == 0 || i == mat.length - 1

                    || j == mat[i].length - 1

• Optimize it by considering only first and last rows and first and the last columns
  • Print the first row of the matrix.
  • Print the last column of the matrix except the first row.
  • Print the last row of the matrix except the last column.
  • Print the first column of the matrix except the first and last row.

Break it down

• four_for_loops
• print_first_row
• print_last_column-first_row
• print_last_row-last_column
• print_first_column-first_row-last_row

Code

# Python program of the above approach
 
# Function to print the boundary elements
# of the matrix in clockwise
def boundaryTraversal(arr, N, M):
 
	# Print the first row
	for i in range(M):
		print(arr[0][i], end = " ");
 
	# Print the last column
	# except the first row
	for i in range(1, N):
		print(arr[i][M - 1], end = " ");
 
	# Print the last row
	# except the last column
	if (N > 1):
 
		# Print the last row
		for i in range(M - 2, -1, -1):
			print(arr[N - 1][i], end = " ");
 
	# Print the first column except
	# the first and last row
	if (M > 1):
 
		# Print the first column
		for i in range(N - 2, 0, -1):
			print(arr[i][0], end = " ");
 
# Driver Code
if __name__ == '__main__':
	arr = [[1, 2, 3],
		[4, 5, 6],
		[7, 8, 9]];
	N = len(arr);
	M = len(arr[0]);
 
	# Function Call
	boundaryTraversal(arr, N, M);