#include

#include $//$memset

#include $//$rand

#include

using namespace std;

class Node

$\{$

private:

int key;

public:

$//$ Array to hold pointers to node of different level

Node $**$forward;

Node$($int$,$ int$)$;

int getKey$()$ const $\{$ return key; $\}$

~Node$()$

$\{$

std::cout $$ "key $"$ key destroyed.

$"$;

$\}$

$\}$;

Node::Node$($int key, int level$)$

$\{$

this$->$key $=$ key;

$//$ Allocate memory to forward

forward $=$ new Node $*[$level $+1]$;

$//$ Fill forward array with $0($NULL$)$

memset$($forward$,0,$ sizeof$($Node $*)*($level $+1))$;

$\}$;

class SkipList

$\{$

$//$ Maximum level for this skip list

int MAXLVL;

float P $=0\mathrm{.}5$;

$//$ current level of skip list

int level;

$//$ pointer to header node

Node $*$header;

public:

SkipList$($int$,$ float$)$;

bool searchElement$($int$)$;

void insertElement$($int$,$ int$=-1)$;

void deleteElement$($int$)$;

void displayList$()$;

int randomLevel$()$;

~SkipList$()$

$\{$

std::cout $$ "skip list destroyed.

$"$;

$\}$

$\}$;

SkipList::SkipList$($int MAXLVL, float P$)$

$\{$

this$->$MAXLVL $=$ MAXLVL;

this$->$P $=$ P;

level $=0$;

$//$ create header node and initialize key to $-1$

header $=$ new Node$($INT$\_$MIN, MAXLVL$)$;

$\}$;

$//$ create random level for node

int SkipList::randomLevel$()$

$\{$

float r $=($float$)$rand$()/$ RAND$\_$MAX;

int lvl $=0$;

while $($r $$ P && lvl $$ MAXLVL$)$

$\{$

lvl$++$;

r $=($float$)$rand$()/$ RAND$\_$MAX;

$\}$

return lvl;

$\}$;

bool SkipList::searchElement$($int key$)$

$\{$

Node $*$current $=$ header;

std::cout$$"Search Path:"; i$--)$

$\{$

while $($current$->$forward$[$i$]$ && current$->$forward$[$i$]->$getKey$()$ key$)$

$\{$

current $=$ current$->$forward$[$i$]$;

$\}$

$\}$

current $=$ current$->$forward$[0]$;

if $($current && current$->$getKey$()==$ key$)$

$\{$

return true;

$\}$

else

$\{$

return false;

$\}$

$\}$;

void SkipList::insertElement$($int key$)$

$\{$

Node $*$current $=$ header;

$//$ create update array and initialize it

Node $*$update$[$MAXLVL $+1]$;

memset$($update$,0,$ sizeof$($Node $*)*($MAXLVL $+1))$;

for $($int i $=$ level; i $>=0$; i$--)$

$\{$

while $($current$->$forward$[$i$]!=$ NULL && current$->$forward$[$i$]->$getKey$()$ key$)$

$\{$

current $=$ current$->$forward$[$i$]$;

$\}$

update$[$i$]=$ current;

$\}$

current $=$ current$->$forward$[0]$;

if $($current $==$ NULL $||$ current$->$getKey$()!=$ key$)$

$\{$

int rlevel $=$ randomLevel$()$;

if $($rlevel $>$ level$)$

$\{$

for $($int i $=$ level $+1$; i $$ rlevel $+1$; i$++)$

update$[$i$]=$ header;

level $=$ rlevel;

$\}$

Node $*$n $=$ new Node$($key$,$ rlevel$)$;

for $($int i $=0$; i rlevel; i$++)$

$\{$

n$->$forward$[$i$]=$ update$[$i$]->$forward$[$i$]$;

update$[$i$]->$forward$[$i$]=$ n;

$\}$

cout $$ "Successfully Inserted key $"$ key

$"$;

$\}$

$\}$;

void SkipList::deleteElement$($int key$)$

$\{$

Node $*$current $=$ header;

$//$ create update array and initialize it

Node $*$update$[$MAXLVL $+1]$;

memset$($update$,0,$ sizeof$($Node $*)*($MAXLVL $+1))$;

for $($int i $=$ level; i $>=0$; i$--)$

$\{$

while $($current$->$forward$[$i$]!=$ NULL &&

current$->$forward$[$i$]->$getKey$()$ key$)$

current $=$ current$->$forward$[$i$]$;

update$[$i$]=$ current;

$\}$

current $=$ current$->$forward$[0]$;

if $($current $!=$ NULL and current$->$getKey$()==$ key$)$

$\{$

for $($int i $=0$; i level; i$++)$

$\{$

if $($update$[$i$]->$forward$[$i$]!=$ current$)$

$\{$

break;

$\}$

update$[$i$]->$forward$[$i$]=$ current$->$forward$[$i$]$;

$\}$

$//$ Remove levels having no elements

while $($level $>0$ && header$->$forward$[$level$]==0)$

$\{$

level$--$;

$\}$

cout $$ "Successfully deleted key $"$ key

$"$;

$\}$

$\}$;

$//$ Display skip list level wise

void SkipList::displayList$()$

$\{$

cout

$*****$Skip List$*****"$

$"$;

for $($int i $=0$; i level; i$++)$

$\{$

Node $*$node $=$ header$->$forward$[$i$]$;

cout $$ "Level $"$ i : $"$;

while $($node $!=$ NULL$)$

$\{$

cout $$ node$->$getKey;

node $=$ node$->$forward$[$i$]$;

$\}$

cout

$"$;

$\}$

$\}$;

$//$ MUST NOT CHANGE THE MAIN FUNCTION

int main$()$

$\{$

srand$($static$\_$cast$($time$($nullptr$)))$; $//$ Seed random number generator

SkipList lst$(3,0\mathrm{.}5)$;

std::cout Insertion $========$

$"$;

lst$.$insertElement$(5,1)$;

lst$.$insertElement$(25,2)$;

lst$.$insertElement$(30,1)$;

lst$.$insertElement$(31,3)$;

lst$.$insertElement$(42,1)$;

lst$.$insertElement$(58,2)$;

lst$.$insertElement$(62,1)$;

lst$.$insertElement$(69,3)$;

lst$.$displayList$()$;

std::cout

$========$ Search $========$

$"$;int key $=31$;

if $($lst$.$searchElement$($key$))$

$\{$

std::cout $$ "Found $"$ key $$ std::endl;

$\}$

else

$\{$

std::cout $$ "Key $"$ key not found.

$"$;

$\}$

std::cout