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import java.util.Scanner;

interface StackInterface $\{$

void push$($T entry$)$;

T pop$()$;

T peek$()$;

boolean isEmpty$()$;

void clear$()$;

$\}$

class LinkedStack implements StackInterface $\{$

private Node topNode;

public LinkedStack$()\{$

topNode $=$ null;

$\}$

public void push$($T newEntry$)\{$

Node newNode $=$ new Node$($newEntry$,$ topNode$)$;

topNode $=$ newNode;

$\}$

public T pop$()\{$

T top $=$ peek$()$;

if $($topNode $!=$ null$)\{$

topNode $=$ topNode.getNextNode$()$;

$\}$

return top;

$\}$

public T peek$()\{$

if $($isEmpty$())\{$

throw new IllegalStateException$("$Stack is empty"$)$;

$\}$

return topNode.getData$()$;

$\}$

public boolean isEmpty$()\{$

return topNode $==$ null;

$\}$

public void clear$()\{$

topNode $=$ null;

$\}$

private class Node $\{$

private T data;

private Node next;

private Node$($T dataPortion$)\{$

this$($dataPortion$,$ null$)$;

$\}$

private Node$($T dataPortion, Node nextNode$)\{$

data $=$ dataPortion;

next $=$ nextNode;

$\}$

private T getData$()\{$

return data;

$\}$

private Node getNextNode$()\{$

return next;

$\}$

$\}$

$\}$

class ArrayStack implements StackInterface $\{$

private T$[]$ stack;

private int topIndex;

private static final int DEFAULT$\_$CAPACITY $=10$;

private static final int MAX$\_$CAPACITY $=10000$;

public ArrayStack$()\{$

this$($DEFAULT$\_$CAPACITY$)$;

$\}$

public ArrayStack$($int initialCapacity$)\{$

@SuppressWarnings$("$unchecked$")$

T$[]$ tempStack $=($T$[])$ new Object$[$initialCapacity$]$;

stack $=$ tempStack;

topIndex $=-1$;

$\}$

public void push$($T newEntry$)\{$

ensureCapacity$()$;

topIndex$++$;

stack$[$topIndex$]=$ newEntry;

$\}$

public T pop$()\{$

if $($isEmpty$())\{$

throw new IllegalStateException$("$Stack is empty"$)$;

$\}$

T top $=$ stack$[$topIndex$]$;

stack$[$topIndex$]=$ null;

topIndex$--$;

return top;

$\}$

public T peek$()\{$

if $($isEmpty$())\{$

throw new IllegalStateException$("$Stack is empty"$)$;

$\}$

return stack$[$topIndex$]$;

$\}$

public boolean isEmpty$()\{$

return topIndex $<0$;

$\}$

public void clear$()\{$

while $(!$isEmpty$())\{$

pop$()$;

$\}$

$\}$

private void ensureCapacity$()\{$

if $($topIndex $>=$ stack.length $-1)\{$

int newLength $=2*$ stack.length;

ensureCapacity$($newLength$)$;

$\}$

$\}$

private void ensureCapacity$($int newLength$)\{$

if $($newLength $>$ MAX$\_$CAPACITY$)\{$

throw new IllegalStateException$("$Attempt to create a stack $"+$

"whose capacity exceeds $"+$

"allowed maximum of $"+$ MAX$\_$CAPACITY$)$;

$\}$

stack $=$ java.util.Arrays.copyOf$($stack$,$ newLength$)$;

$\}$

$\}$

public class StackMath $\{$

public static void main$($String$[]$ args$)\{$

Scanner scanner $=$ new Scanner$($System$.$in$)$;

System.out.println$("$Enter an infix or postfix expression:"$)$;

String expression $=$ scanner.nextLine$().$trim$()$;

System.out.println$("$Infix: $"+$ postfix$2$infix$($expression$))$;

System.out.println$("$Postfix: $"+$ infix$2$postfix$($expression$))$;

System.out.println$("$Evaluation $($infix$)$: $"+$ evaluateInfix$($expression$))$;

System.out.println$("$Evaluation $($postfix$)$: $"+$ evaluatePostfix$($expression$))$;

$\}$

public static String infix$2$postfix$($String infix$)\{$

$//$ Implement conversion from infix to postfix

return $""$;

$\}$

public static String postfix$2$infix$($String postfix$)\{$

$//$ Implement conversion from postfix to infix

return $""$;

$\}$

public static int evaluatePostfix$($String postfix$)\{$

$//$ Implement evaluation of postfix expression

return $0$;

$\}$

public static int evaluateInfix$($String infix$)\{$

$//$ Implement evaluation of infix expression

return $0$;

$\}$

$\}$