Given an n x m matrix, write an algorithm to print all the elements that lie on its outer edges. These include the elements in the first row, the last row, the first column, and the last column of the matrix.

Hint

Create an empty list to record the order in which the algorithm will visit positions. Start at the top-right corner of the matrix. Move along the top row from right to left. Move down the rightmost column from top to bottom. Move along the bottom row from right to left. Move up the leftmost column from bottom to top. As the algorithm moves through these sides of the matrix, it adds each visited position to the list of steps.

# Python implementation

matrix = [
  [5, 1, 3, 4, 1],
  [6, 9, 6, 5, 1],
  [5, 3, 3, 7, 1],
  [1, 9, 6, 5, 3]
]
output = []
h = len(matrix)
w = len(matrix[0])

for i in range(w):
  output.append(matrix[0][i])

for i in range(1, h):
  output.append(matrix[i][w - 1])

for i in range(w - 2, -1, -1):
  output.append(matrix[h-1][i])

for i in range(h - 2, 0, -1):
  output.append(matrix[i][0])

print(output)

// Javascript implementation

const matrix = [
  [5, 1, 3, 4, 1],
  [6, 9, 6, 5, 1],
  [5, 3, 3, 7, 1],
  [1, 9, 6, 5, 3]
];
const output = [];
const h = matrix.length;
const w = matrix[0].length;

for (let i = 0; i < w; i++) {
  output.push(matrix[0][i]);
}

for (let i = 1; i < h; i++) {
  output.push(matrix[i][w - 1]);
}

for (let i = w - 2; i >= 0; i--) {
  output.push(matrix[h-1][i]);
}

for (let i = h - 2; i >= 1; i--) {
  output.push(matrix[i][0]);
}

console.log(output);

Print boundary elements of a matrix

Hint