please write pseudocode using Cormen chapter $2$ class Stack $\{$

constructor$()\{$

this.items $=[]$;

$\}$

push$($element$)\{$

this.items.push$($element$)$;

$\}$

pop$()\{$

if $($this$.$isEmpty$())$ return "Underflow";

return this.items.pop$()$;

$\}$

peek$()\{$

return this.items$[$this$.$items.length $-1]$;

$\}$

isEmpty$()\{$

return this.items.length $===0$;

$\}$

$\}$

class PostfixEvaluator $\{$

constructor$()\{$

this.stack $=$ new Stack$()$;

this.variables $=\{\}$;

$\}$

evaluatePostfix$($expression$)\{$

const tokens $=$ expression.split$(\text{'}\text{'})$;

for $($let i $=0$; i $<$ tokens.length; i$++)\{$

const token $=$ tokens$[$i$]$;

if $(!$isNaN$($parseFloat$($token$)))\{$

this.stack.push$($parseFloat$($token$))$;

$\}$ else if $($token in this.variables$)\{$

this.stack.push$($this$.$variables$[$token$])$;

$\}$ else if $($this$.$isOperator$($token$))\{$

const operand$2=$ this.stack.pop$()$;

const operand$1=$ this.stack.pop$()$;

const result $=$ this.calculate$($token$,$ operand$1,$ operand$2)$;

this.stack.push$($result$)$;

$\}$ else if $($token $!==\text{'}=\text{'})\{$

throw new Error$(\text{'}$Invalid token: $\text{'}+$ token$)$;

$\}$

$\}$

return this.stack.pop$()$;

$\}$

isOperator$($token$)\{$

return token $===\text{'}+\text{'}||$ token $===\text{'}-\text{'}||$ token $===\text{'}*\text{'}||$ token $===\text{'}/\text{'}$;

$\}$

calculate$($operator$,$ operand$1,$ operand$2)\{$

switch $($operator$)\{$

case $\text{'}+\text{'}$:

return operand$1+$ operand$2$;

case $\text{'}-\text{'}$:

return operand$1-$ operand$2$;

case $\text{'}*\text{'}$:

return operand$1*$ operand$2$;

case $\text{'}/\text{'}$:

if $($operand$2===0)$ throw new Error$(\text{'}$Division by zero'$)$;

return operand$1/$ operand$2$;

default:

throw new Error$(\text{'}$Invalid operator'$)$;

$\}$

$\}$

setVariable$($name$,$ value$)\{$

this.variables$[$name$]=$ value;

$\}$

$\}$