Explain whether or not you would expect any difference in the best$-$case and worst$-$case complexities of your function $`$longest$\_$common$\_$substring$`.$

Analyse the worst$-$case complexity of your function. You may find it convenient to define L $=`|$left$|`$ and R $=`|$right$|`$ and to express the complexity in terms of those values. We have used uppercase letters to avoid confusing lowercase $`\text{'}$l$\text{'}`$ with other characters.

You should use Big$-$Theta notation $($Section $2\mathrm{.}7)$ or Big$-$Oh notation $($Section $13\mathrm{.}3\mathrm{.}3)$ as appropriate. Complexity of sequence operations $($which applies to strings$)$ is given in Section $4\mathrm{.}9\mathrm{.}1.$