How to write a algorithm here

Answer 1

One does not write algorithmns.
One creates algorithmns and writes codes with them

Answer 2

algorithms are basic rule according to which we can calculate something or do some task.
In computer algorithms are basically a set of instruction which can do some task.

this will clear your doubts
https://youtu.be/6hfOvs8pY1k

algorithms are not something big or something different as i earlier used to think. They are just like mathematical formulas.