matrix of size n x n with all elements set to 0.num to 1.top, bottom, left, and right.num is less than or equal to n^2, repeat the following steps:
a. Traverse from left to right along the top row and fill the cells with num.
b. Increment top to move to the next inner layer.
c. Traverse from top to bottom along the right column and fill the cells with num.
d. Decrement right to narrow the layer.
e. Traverse from right to left along the bottom row and fill the cells with num.
f. Decrement bottom to move to the next inner layer.
g. Traverse from bottom to top along the left column and fill the cells with num.
h. Increment left to narrow the layer.matrix.