I am confused between sub-quadratic and quadratic algorithm. I know it is quadratic when big O is equal to n squared. Then what is a subquadratic algorithm?
Subquadratic denotes an algorithm whose complexity ~o(n^2), using not-o notation . This means that complexity is growing much slower than n^2. It can be anything from linear to almost quadratic.
~o(n^2)
n^2
In unprofessional terms, it is something between linear and quadratic, for example n^2/logn.
n^2/logn