$2)$ If instead L is a doubly linked list, refer to the example code provided above, fill in the code blocks tofulfill the wanted purposes. a$.$ Insert a node s after the $2$ nd node $(5\%)$ b$.$ Insert a node s before the last node $(5\%)$ c$.$ Swap the positions of the first and the last node. Do not modify the values $($data$)$ of the nodes $(10\%)$