class SLNode:

$"""$

Singly Linked List Node class

DO NOT CHANGE THIS CLASS IN ANY WAY

$"""$

def $\_\_$init$\_\_($self$,$ value: object, next$=$None$)->$ None:

self.value $=$ value

self.next $=$ next

from SLNode import $*$

class SLLException$($Exception$)$:

$"""$

Custom exception class to be used by Singly Linked List

DO NOT CHANGE THIS CLASS IN ANY WAY

$"""$

pass

class LinkedList:

def $\_\_$init$\_\_($self$,$ start$\_$list$=$None$)->$ None:

$"""$

Initialize new linked list

DO NOT CHANGE THIS METHOD IN ANY WAY

$"""$

self.$\_$head $=$ SLNode$($None$)$

# populate SLL with initial values $($if provided$)$

# before using this feature, implement insert$\_$back$()$ method

if start$\_$list is not None:

for value in start$\_$list:

self.insert$\_$back$($value$)$

def $\_\_$str$\_\_($self$)->$ str:

$"""$

Return content of singly linked list in human$-$readable form

DO NOT CHANGE THIS METHOD IN ANY WAY

$"""$

out $=\text{'}$SLL $[\text{'}$

node $=$ self.$\_$head.next

while node:

out $+=$ str$($node$.$value$)$

if node.next:

out $+=\text{'}->\text{'}$

node $=$ node.next

out $+=\text{'}]\text{'}$

return out

def length$($self$)->$ int:

$"""$

Return the length of the linked list

DO NOT CHANGE THIS METHOD IN ANY WAY

$"""$

length $=0$

node $=$ self.$\_$head.next

while node:

length $+=1$

node $=$ node.next

return length

def is$\_$empty$($self$)->$ bool:

$"""$

Return True is list is empty, False otherwise

DO NOT CHANGE THIS METHOD IN ANY WAY

$"""$

return not self.$\_$head.next

# $------------------------------------------------------------------$ #

def insert$\_$front$($self$,$ value: object$)->$ None:

$"""$

TODO: Write this implementation

$"""$

pass

def insert$\_$back$($self$,$ value: object$)->$ None:

$"""$

TODO: Write this implementation

$"""$

pass

def insert$\_$at$\_$index$($self$,$ index: int, value: object$)->$ None:

$"""$

TODO: Write this implementation

$"""$

pass

def remove$\_$at$\_$index$($self$,$ index: int$)->$ None:

$"""$

TODO: Write this implementation

$"""$

pass

def remove$($self$,$ value: object$)->$ bool:

$"""$

TODO: Write this implementation

$"""$

pass

def count$($self$,$ value: object$)->$ int:

$"""$

TODO: Write this implementation

$"""$

pass

def find$($self$,$ value: object$)->$ bool:

$"""$

TODO: Write this implementation

$"""$

pass

def slice$($self$,$ start$\_$index: int, size: int$)->$ "LinkedList":

$"""$

TODO: Write this implementation

$"""$

pass

if $\_\_$name$\_\_=="\_\_$main$\_\_"$:

print$("$

# insert$\_$front example $1")$

test$\_$case $=["$A$","$B$","$C$"]$

lst $=$ LinkedList$()$

for case in test$\_$case:

lst$.$insert$\_$front$($case$)$

print$($lst$)$

print$("$

# insert$\_$back example $1")$

test$\_$case $=["$C$","$B$","$A$"]$

lst $=$ LinkedList$()$

for case in test$\_$case:

lst$.$insert$\_$back$($case$)$

print$($lst$)$

print$("$

# insert$\_$at$\_$index example $1")$

lst $=$ LinkedList$()$

test$\_$cases $=[(0,"$A$"),(0,"$B$"),(1,"$C$"),(3,"$D$"),(-1,"$E$"),(5,"$F$")]$

for index, value in test$\_$cases:

print$("$Inserted$",$ value, $"$at index", index, $"$: $",$ end$="")$

try:

lst$.$insert$\_$at$\_$index$($index$,$ value$)$

print$($lst$)$

except Exception as e:

print$($type$($e$))$

print$("$

# remove$\_$at$\_$index example $1")$

lst $=$ LinkedList$([1,2,3,4,5,6])$

print$($f$"$Initial LinkedList : $\{$lst$\}")$

for index in $[0,2,0,2,2,-2]$:

print$("$Removed at index", index, $"$: $",$ end$="")$

try:

lst$.$remove$\_$at$\_$index$($index$)$

print$($lst$)$

except Exception as e:

print$($type$($e$))$

print$("$

# remove example $1")$

lst $=$ LinkedList$([1,2,3,1,2,3,1,2,3])$

print$($f$"$Initial LinkedList, Length: $\{$lst$.$length$()\}$

$\{$lst$\}")$

for value in $[7,3,3,3,3]$:

print$($f$"$remove$(\{$value$\})$: $\{$lst$.$remove$($value$)\},$ Length: $\{$lst$.$length$()\}"$

f$"$

$\{$lst$\}")$

print$("$

# remove example $2")$

lst $=$ LinkedList$([1,2,3,1,2,3,1,2,3])$

print$($f$"$Initial LinkedList, Length: $\{$lst$.$length$()\}$

$\{$lst$\}")$

for value in $[1,2,3,1,2,3,3,2,1]$:

print$($f$"$remove$(\{$value$\})$: $\{$lst$.$remove$($value$)\},$ Length: $\{$lst$.$length$()\}"$

f$"$

$\{$lst$\}")$

print$("$

# count example $1")$

lst $=$ LinkedList$([1,2,3,1,2,2])$

print$($lst$,$ lst$.$count$(1),$ lst$.$count$(2),$ lst$.$count$(3),$ lst$.$count$(4))$

print$("$

# find example $1")$

lst $=$ LinkedList$(["$Waldo$",$ "Clark Kent", "Homer", "Santa Claus"$])$

print$($lst$)$

print$($lst$.$find$("$Waldo$"))$

print$($lst$.$find$("$Superman$"))$

print$($lst$.$find$("$Santa Claus"$))$

print$("$

# slice example $1")$

lst $=$ LinkedList$([1,2,3,4,5,6,7,8,9])$

ll$\_$slice $=$ lst$.$slice$(1,3)$

print$("$Source:$",$ lst$)$

print$("$Start: $1$ Size: $3$ :$",$ ll$\_$slice$)$

ll$\_$slice.remove$\_$at$\_$index$(0)$

print$("$Removed at index $0$ :$",$ ll$\_$slice$)$

print$("$

# slice example $2")$

lst $=$ LinkedList$([10,11,12,13,14,15,16])$

print$("$Source:$",$ lst$)$

slices $=[(0,7),(-1,7),(0,8),(2,3),(5,0),(5,3),(6,1)]$

for index, size in slices:

print$("$Start:$",$ index, "Size:", size, end$="")$

try:

print$("$ :$",$ lst$.$slice$($index$,$ size$))$

except:

print$("$ : exception occurred."$)$