OT: CSES Number Spiral algorithm

I don't have a C question, but rather I'd like input about algorithmic approaches.
https://cses.fi/problemset/task/1071
It's an 'infinite grid'.  You have to find the value at rows-columns from 1 to 10^9.
First thing you notice about the 5x5 grid is the values in odd-numbered columns begin with the square of the column number, and the values in even-numbered rows begin with the square of the row number.
I followed the number pattern and built a grid in Excel and expanded it to 10x10 for more testing.
https://imgur.com/x4VymmA
Then coded 4 conditions      solution
1. row <= col and col odd    (col * col) - row + 1
2. row <= col and col even   ((col-1) * (col-1)) + row
3. row >  col and row odd    ((row-1) * (row-1)) + col
4. row >  col and row even   (row * row) - col + 1
My full C code submission was accepted the first time.
How would you have done it?