import java.util.$*$;

public class LabProgram $\{$

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

$//$ Get user input

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

String userInput $=$ reader.nextLine$()$;

$//$ Parse into a binary tree

Node userRoot $=$ Node.parse$($userInput$)$;

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

Node badNode $=$ BSTChecker.checkBSTValidity$($userRoot$)$;

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

System.out.print$($String$.$valueOf$($badNode$.$key$))$;

System.out.print$("$

$")$;

$\}$

else $\{$

System.out.print$("$No violation"$)$;

System.out.print$("$

$")$;

$\}$

$\}$

else $\{$

System.out.print$("$Failed to parse input tree"$)$;

System.out.print$("$

$")$;

$\}$

reader.close$()$;

$\}$

$\}$

import java.util.$*$;

public class Node $\{$

private static String removeLeadingWhitespace$($String str$)\{$

int i $=0$;

while $($i $<mtext\; id="EditorElement\_938098"></mtext><mi\; id="EditorElement\_938099">(</mi>$int$)$ str$.$length$())\{$

$//$ If the character at index i is not whitespace, then return the

$//$ substring that starts at i

if $(!$Character.isWhitespace$($str$.$charAt$($i$)))\{$

return str$.$substring$($i$)$;

$\}$

i$++$;

$\}$

$//$ Completing the loop means the entire string is whitespace

return new String$()$;

$\}$

public int key;

public Node left;

public Node right;

public Node$($int nodeKey, Node leftChild$)\{$

this$($nodeKey$,$ leftChild, null$)$;

$\}$

public Node$($int nodeKey$)\{$

this$($nodeKey$,$ null, null$)$;

$\}$

public Node$($int nodeKey, Node leftChild, Node rightChild$)\{$

key $=$ nodeKey;

left $=$ leftChild;

right $=$ rightChild;

$\}$

public void close$()\{$

$\}$

$//$ Counts the number of nodes in this tree

public int count$()\{$

int leftCount $=0$;

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

leftCount $=$ left.count$()$;

$\}$

int rightCount $=0$;

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

rightCount $=$ right.count$()$;

$\}$

return $1+$ leftCount $+$ rightCount;

$\}$

$//$ Inserts the new node into the tree.

public void insert$($Node node$)\{$

Node currentNode $=$ this;

while $($currentNode $!=$ null$)\{$

if $($node$.$key $$ currentNode.key$)\{$

if $($currentNode$.$left $!=$ null$)\{$

currentNode $=$ currentNode.left;

$\}$

else $\{$

currentNode.left $=$ node;

currentNode $=$ null;

$\}$

$\}$

else $\{$

if $($currentNode$.$right $!=$ null$)\{$

currentNode $=$ currentNode.right;

$\}$

else $\{$

currentNode.right $=$ node;

currentNode $=$ null;

$\}$

$\}$

$\}$

$\}$

public void insertAll$($final ArrayList keys$)\{$

for $($int key : keys$)\{$

insert$($new Node$($key$))$;

$\}$

$\}$

public static Node parse$($String treeString$)\{$

$//$ A node is enclosed in parentheses with a either just a key: $($key$),$

$//$ or a key, left child, and right child triplet: $($key$,$ left, right$).$ The

$//$ left and right children, if present, can be either a nested node or

$//$ "null".

$//$ Remove leading whitespace first

treeString $=$ Node.removeLeadingWhitespace$($treeString$)$;

$//$ The string must be non$-$empty, start with $"(",$ and end with $")"$

if $(0==$ treeString.length$()||$ treeString.charAt$(0)!=\text{'}(\text{'}$

$||$ treeString.charAt$($treeString$.$length$()-1)!=\text{'})\text{'})\{$

return null;

$\}$

$//$ Parse between parentheses

treeString $=$ treeString.substring$(1,$ treeString.length$()-1)$;

$//$ Find non$-$nested commas

ArrayList commaIndices $=$ new ArrayList$()$;

int parenCounter $=0$;

for $($int i $=0$; i $<mtext\; id="EditorElement\_940437"></mtext><mi\; id="EditorElement\_940438">(</mi>$int$)$ treeString.length$()$; i$++)\{$

char character $=$ treeString.charAt$($i$)$;

if $(\text{'}(\text{'}==$ character$)\{$

parenCounter$++$;

$\}$

else if $(\text{'})\text{'}==$ character$)\{$

parenCounter$--$;

$\}$

else if $(\text{'},\text{'}==$ character && $0==$ parenCounter$)\{$

commaIndices.add$($i$)$;

$\}$

$\}$

$//$ If no commas, treeString is expected to be just the node's key

if $(0==$ commaIndices.size$())\{$

return new Node$($Integer$.$parseInt$($treeString$))$;

$\}$

$//$ If number of commas is not $2,$ then the string's format is invalid

if $(2!=$ commaIndices.size$())\{$

return null;

$\}$

$//$ "Split" on comma

int i$1=$ commaIndices.get$(0)$;

int i$2=$ commaIndices.get$(1)$;

String piece$1=$ treeString.substring$(0,$ i$1)$;

String piece$2=$ treeString.substring$($i$1+1,$ i$2)$;

String piece$3=$ treeString.substring$($i$2+1)$;

$//$ Make the node with just the key

Node nodeToReturn $=$ new Node$($Integer$.$parseInt$($piece$1))$;

$//$ Recursively parse children

nodeToReturn.left $=$ Node.parse$($piece$2)$;

nodeToReturn.right $=$ Node.parse$($piece$3)$;

return nodeToReturn;

$\}$

$\}$

$8$:Unit test

Invalid tree with right child linking to ancestor

Test feedback

checkBSTValidity$()$ returned a node that is not the BST rule$-$violating node

$9$:Unit test

Invalid tree with left child linking to parent

Test feedback

checkBSTValidity$()$ returned a node that is not the BST rule$-$violating node

$10$:Unit test

Invalid tree with left child linking to ancestor

checkBSTValidity$()$ returned a node that is not the BST rule$-$violating node