Traversing the Outer Edges

To traverse the outer edge, we have to follow the given sequence:

1. Move right
2. Move down
3. Move left
4. Move up

Once we have moved entirely right, we can increment rowLower. Similarly, once we have traversed down the right-most column we can decrement colUpper. Therefore, to traverse the entire matrix in spiral order, we can follow the given algorithm.

The entire process is shown in the figure below:

Here, we share some pseudo-code to help make sense of the logic involved.

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Method: traverse

Input: mxn matrix

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Initialize: 

1. rowLower = 0

2. rowUpper = m-1

3. colLower = 0

4. colUpper = n-1

​

while the entire matrix is not traversed repeat

{

    i.    Traverse the row with index rowLower

    ii.   rowLower ++

    iii.  Traverse the column with index colUpper

    iv.   colUpper --

    v.    Traverse the row with index rowUpper

    vi.   rowUpper --

    vii.  Traverse the column with index colLower

    viii. colLower ++

}