I'm trying to figure out how to do the different traversals through an expression tree. For example, if I type in " - + 10 * 2 8 3 ", I want it to print out the prefix, postfix, and infix versions of that expression.
I also need to calculate the result of the expression through a postorder traversal, which should be the evaluate function.
However, when I run my program, I only get the first character of each expression. Is my understanding of how these traversals work wrong?
EDIT: Following suggestions, I saved the result of the buildtree and also changed sc.next to sc.nextLine.
Also, every method should be recursive.
Given "- + 10 * 2 8 3", the expected answer would be:
prefix expression:
- + 10 * 2 8 3
postfix expression:
10 2 8 * + 3 -
infix expression:
( ( 10 + ( 2 * 8 ) ) - 3 )
Result = 23
I understand I haven't implemented anything with parentheses for the infix expression, but that's okay for now.
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter a prefix expression: ");
Node root = buildTree(sc);
System.out.println("prefix expression: ");
infix(root);
System.out.println("postfix expression: ");
postfix(root);
System.out.println("infix expression: ");
infix(root);
System.out.print("Result = ");
evaluate(root);
}
static Node buildTree(Scanner sc) {
Node n = new Node(null);
int i = 0;
String prefixExpression = sc.nextLine();
String[] temp = prefixExpression.split(" ");
if(n.isLeaf()) {
n.value = temp[i];
n.left = null;
n.right = null;
i++;
}
return n;
}
static void infix(Node node) {
if(node.isLeaf()){
System.out.println(node.value);
}
else {
infix(node.left);
System.out.println(node.value + " ");
infix(node.right);
}
}
void prefix(Node node) {
if(node.isLeaf()){
System.out.println(node.value);
}
else {
switch(node.value) {
case "+":
System.out.print("+");
break;
case "-":
System.out.print("-");
break;
case "*":
System.out.print("*");
break;
case "/":
System.out.print("/");
break;
}
}
prefix(node.left);
System.out.print(" ");
prefix(node.right);
}
static void postfix(Node node) {
if(node.isLeaf()){
System.out.println(node.value);
}
else {
postfix(node.left);
postfix(node.right);
switch (node.value) {
case "+":
System.out.print("+");
break;
case "-":
System.out.print("-");
break;
case "*":
System.out.print("*");
break;
case "/":
System.out.print("/");
break;
}
}
}
public static int evaluate(Node node) {
if(node.isLeaf()) {
return Integer.parseInt(node.value);
}
else {
int leftHandSide = evaluate(node.getLeft());
int rightHandSide = evaluate(node.getRight());
String operator = node.getValue();
if("+".equals(operator)) {
return leftHandSide + rightHandSide;
}
else if("-".equals(operator)) {
return leftHandSide - rightHandSide;
}
else if("*".equals(operator)) {
return leftHandSide * rightHandSide;
}
else if("/".equals(operator)) {
return leftHandSide / rightHandSide;
}
else {
System.out.println("Unexpected problem. Error.");
}
return 0;
}
}
}
Here is Node.java, There's getters and setters too.
public class Node<E> {
String value;
Node<E> left;
Node<E> right;
Node(String value){
left = null;
right = null;
this.value = value;
}
Node(String value, Node<E> left, Node<E> right) {
this.value = value;
this.left = left;
this.right = right;
}
boolean isLeaf() {
return (left == null && right == null);
}
EDIT:
Since your question says "How to do different traversals of an expression tree?, The problem I can see in your code is building the tree ( i.e. buildTree() method).
In order to correct this, I have used buildExpressionTree(array) method to convert your prefix input to an expression tree using Stack data structure.
Construction of Expression Tree:
For constructing expression tree I have use a stack. Since in your case input is in prefix form so Loop in reverse through input expression and do following for every character.
If character is operand push that into stack
If character is operator pop two values from stack make them its
child and push current node again.
At the end only element of stack will be root of expression tree.
Also while printing different traversals, you do not need all those if conditions to check for different operators.You can simply do the traversal as shown in my code below.
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a prefix expression: ");
String prefixExpression = sc.nextLine();
String[] temp = prefixExpression.split(" ");
Node n = null;
n = buildExpressionTree(temp);
System.out.println("prefix expression: ");
prefix(n);
System.out.println();
System.out.println("postfix expression: ");
postfix(n);
System.out.println();
System.out.println("infix expression: ");
infix(n);
System.out.println();
int result = evaluate(n);
System.out.print("Result = "+ result);
}
static Node buildExpressionTree(String[] input) {
Stack<Node> st = new Stack();
Node t, t1, t2;
// Traverse through every character of
// input expression
for (int i = (input.length-1); i >= 0; i--) {
// If operand, simply push into stack
if (isNumber(input[i])) {
t = new Node(input[i]);
st.push(t);
} else // operator
{
t = new Node(input[i]);
// Pop two top nodes
// Store top
t1 = st.pop(); // Remove top
t2 = st.pop();
// make them children
t.left = t1;
t.right = t2;
st.push(t);
}
}
t = st.peek();
st.pop();
return t;
}
static boolean isNumber(String s) {
boolean numeric = true;
try {
Integer num = Integer.parseInt(s);
} catch (NumberFormatException e) {
numeric = false;
}
return numeric;
}
static void infix(Node node) {
if( null == node) {
return;
}
infix(node.left);
System.out.print(node.value + " ");
infix(node.right);
}
static void prefix(Node node) {
if( null == node) {
return;
}
System.out.print(node.value+ " ");
prefix(node.left);
prefix(node.right);
}
static void postfix(Node node) {
if( null == node) {
return;
}
postfix(node.left);
postfix(node.right);
System.out.print(node.value+ " ");
}
public static int evaluate(Node node) {
if(node.isLeaf()) {
return Integer.parseInt(node.value);
}
else {
int leftHandSide = evaluate(node.left);
int rightHandSide = evaluate(node.right);
String operator = node.value;
if("+".equals(operator)) {
return leftHandSide + rightHandSide;
}
else if("-".equals(operator)) {
return leftHandSide - rightHandSide;
}
else if("*".equals(operator)) {
return leftHandSide * rightHandSide;
}
else if("/".equals(operator)) {
return leftHandSide / rightHandSide;
}
else {
System.out.println("Unexpected problem. Error.");
}
return 0;
}
}
OUTPUT:
Enter a prefix expression:
- + 10 * 2 8 3
prefix expression:
- + 10 * 2 8 3
postfix expression:
10 2 8 * + 3 -
infix expression:
10 + 2 * 8 - 3
Result = 23
Related
Hello I am getting a logical error where it isn't saluting the postfix correctly. For example:
-16.0
16.01171875
-16.25
I do not know why am getting negative numbers It is supposed to be:
25.0
9.71
17.0
I think Im doing the pushing wrong but I don't know where it could be wrong. Here's the method:
static double evaluatePostfix(String postfix){
Stack stack = new Stack();
int size =postfix.length();
for(int i = 0; i<postfix.length(); i++){
if(postfix.charAt(i) == '+'|| postfix.charAt(i) == '-'||postfix.charAt(i) == '*'||postfix.charAt(i) == '/'){
double value =0 ;
double value2 = 0 ;
String str = stack.pop().toString();
String str2 = stack.pop().toString();
value = Double.valueOf(str).doubleValue();
value2 = Double.valueOf(str2).doubleValue();
switch(postfix.charAt(i))
{
case '+': stack.push(value2 + value);
break;
case '-': stack.push(value2 - value);
break;
case '*': stack.push(value2 * value );
break;
case '/': stack.push(value2 / value);
break;
}
}
else if (postfix.charAt(i) >= 'a' && postfix.charAt(i) <= 'z'){
System.out.println("bad Character");
return Double.NEGATIVE_INFINITY;
}
else{
double operand = (double)(postfix.charAt(i) - '0');
stack.push(operand);
size++;
}
}
return (double)(stack.pop());
}
I have to convert the popping into doubles because I can't create a double stack and I must use a stack class instead without importing any java.utils.
Here's the stack class
public class Stack{
private Node top;
public Stack() {
top = null;
}
public boolean isEmpty(){
return (top ==null);
}
public void push(Object newItem){
top = new Node(newItem, top);
}
public Object pop(){
if (isEmpty()){
System.out.println(
"Trying to pop when stack is empty");
return null;
}else{
Node temp = top;
top = top.next;
return temp.info;
}
}
void popAll(){
top = null;
}
public Object peek(){
if (isEmpty()){
System.out.println(
"Trying to peek when stack is empty");
return null;
}else{
return top.info;
}
}
Here's the input:
10 2 / 5 *
5 10 - 3 9 - * 5 4 - 4 2 / + / 2 27 + 300 3 / / -
15 8 4 / +
This question already has answers here:
What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?
(26 answers)
Closed 4 years ago.
I'm working on a Binary Search Tree assignment, and I was testing what I thought was the finished product when I saw that when I added a number to the tree and then tried to check it's predecessor/successor (by putting it into an array using in order traverse and then checking the index before/after it) it just...didn't work. Any time I try to check the predecessor/successor of a value I just put in the middle of the tree, it wigs out with an ArrayIndexOutOfBoundsException. Important note is that simply printing out using inordertraverse (called printInOrder in the code) works perfectly.
Since printing the inorder traverse works, I can assume my tree isn't the problem. The only other thing is the array, right? Am I missing something obvious?
Here's the code!
public class BST implements BSTInterface
{
//Variables/Fields
private BNode root;
//Constructors
public BST(int data)
{
root = new BNode(data);
}
//Public Methods
public boolean add(int data)
{
if(!contains(data))
{
root = addEntry(root, data);
return true;
}
else
return false;
}
public boolean contains(int data)
{
return containsNode(root, data);
}
public boolean remove(int data)
{
if(contains(data))
{
root = deleteNode(root, data);
return true;
}
else
return false;
}
public int[] toArray()
{
int[] output = new int[root.numNodes()];
inorderTraverse(output, 0, root);
return output;
}
public void printInOrder()
{
printIn(root);
}
public void printPreOrder()
{
printPre(root);
}
public void printPostOrder()
{
printPost(root);
}
//Private methods/classes
private class BNode
{
private int data;
private BNode leftChild;
private BNode rightChild;
public BNode(int data)
{
this.data = data;
leftChild = null;
rightChild = null;
}
public int getData()
{
return data;
}
public void setData(int newData)
{
data = newData;
}
public BNode getLeftChild()
{
return leftChild;
}
public BNode getRightChild()
{
return rightChild;
}
public void setRightChild(BNode node)
{
rightChild = node;
}
public void setLeftChild(BNode node)
{
leftChild = node;
}
public int numNodes()
{
int leftNum = 0;
int rightNum = 0;
if(leftChild != null)
leftNum = leftChild.numNodes();
if(rightChild != null)
rightNum = rightChild.numNodes();
return 1+leftNum+rightNum;
}
}
private BNode addEntry(BNode current, int data)
{
if(current == null)
return new BNode(data);
if(data < current.getData())
current.setLeftChild(addEntry(current.getLeftChild(), data));
else if(data > current.getData())
current.setRightChild(addEntry(current.getRightChild(), data));
return current;
}
private boolean containsNode(BNode current, int entry)
{
if(current == null)
return false;
if(entry == current.getData())
return true;
if(entry < current.getData())
return containsNode(current.getLeftChild(), entry);
else
return containsNode(current.getRightChild(), entry);
}
private BNode deleteNode(BNode current, int data)
{
if(current == null)
return null;
if(data == current.getData())
{
if(current.getLeftChild() == null && current.getRightChild() == null) //No children
return null;
if(current.getRightChild() == null) //Only right child
return current.getLeftChild();
if(current.getLeftChild() == null) //Only left child
return current.getRightChild();
int smallestChild = findSmallest(current.getRightChild());
current.setData(smallestChild);
current.setRightChild(deleteNode(current.getRightChild(), smallestChild));
return current;
}
if(data < current.getData())
{
current.setLeftChild(deleteNode(current.getLeftChild(), data));
return current;
}
else
current.setRightChild(deleteNode(current.getRightChild(), data));
return current;
}
private int findSmallest(BNode root)
{
return root.getLeftChild() == null ? root.getData() : findSmallest(root.getLeftChild());
}
private void inorderTraverse(int[] array, int count, BNode node)
{
if(node != null)
{
inorderTraverse(array, count, node.getLeftChild());
array[count] = node.getData();
count++;
inorderTraverse(array, count, node.getRightChild());
}
}
private void printIn(BNode node)
{
if(node != null)
{
printIn(node.getLeftChild());
System.out.print(node.getData() + " ");
printIn(node.getRightChild());
}
}
private void printPre(BNode node)
{
if(node != null)
{
System.out.print(node.getData() + " ");
printPre(node.getLeftChild());
printPre(node.getRightChild());
}
}
private void printPost(BNode node)
{
if(node != null)
{
printPost(node.getLeftChild());
printPost(node.getRightChild());
System.out.print(node.getData() + " ");
}
}
}
along with the driver program:
import java.util.Scanner;
public class BSTDemoReel
{
public static void main(String[] args)
{
System.out.println("This search tree only handles integers! Thanks in advance!\n\n");
Scanner keyboard = new Scanner(System.in);
//Variables
String input;
String choice = "";
int num;
int index;
boolean found;
//Starting
System.out.println("Please enter the initial sequence of values:\n");
input = keyboard.nextLine();
String[] splitInput = input.split(" ");
int[] intInputArray = new int[splitInput.length];
for(int count = 0; count < splitInput.length; count++)
{
intInputArray[count] = Integer.parseInt(splitInput[count]);
}
BST searchTree = new BST(intInputArray[0]);
for(int count = 1; count < intInputArray.length; count++)
{
searchTree.add(intInputArray[count]);
}
System.out.print("Pre-order: ");
searchTree.printPreOrder();
System.out.println();
System.out.print("In-order: ");
searchTree.printInOrder();
System.out.println();
System.out.print("Post-order: ");
searchTree.printPostOrder();
System.out.println();
//Menu
while(!choice.equals("E"))
{
System.out.print("Command? ");
choice = keyboard.next();
choice = choice.toUpperCase();
switch(choice)
{
case "I": num = keyboard.nextInt();
if(searchTree.contains(num))
System.out.println(num + " already exists. Please try again.");
else
{
searchTree.add(num);
System.out.print("In-order: ");
searchTree.printInOrder();
System.out.println();
}
break;
case "D": num = keyboard.nextInt();
if(!searchTree.contains(num))
System.out.println(num + " does not exist. Please try again.");
else
{
searchTree.remove(num);
System.out.print("In-order: ");
searchTree.printInOrder();
System.out.println();
}
break;
case "P": num = keyboard.nextInt();
if(searchTree.contains(num))
{
int[] array = searchTree.toArray();
index = 0;
found = false;
while(!found)
{
if(num == array[index])
found = true;
else
index++;
}
if(index != 0)
System.out.println(array[index-1]);
else
System.out.println("That was the first one!");
}
else
System.out.println(num + " does not exist! Please try again!");
break;
case "S": num = keyboard.nextInt();
if(searchTree.contains(num))
{
int[] array = searchTree.toArray();
index = 0;
found = false;
while(!found)
{
if(num == array[index])
found = true;
else
index++;
}
if(index != array.length-1)
System.out.println(array[index+1]);
else
System.out.println("That was the last one!");
}
else
System.out.println(num + " does not exist! Please try again!");
break;
case "E": System.out.println("Was a tricky one! Thanks for playing ;P");
break;
case "H": System.out.println("I Insert a value\n" +
"D Delete a value\n" +
"P Find predecessor\n" +
"S Find successor\n" +
"E Exit the program\n" +
"H Display this message");
break;
default: System.out.println("Invalid command. Type H for help.");
break;
}
}
keyboard.close();
}
}
If you add a couple of lines of code to print out the array returned by searchTree.toArray() before you enter the while loop that examines the array to find the value specified with the P or S commands then you'll see the cause of the problem. The array is not filled in correctly. The desired value might not be present in the array, which means that found will never become True and the while loop will continue to increment index until it exceeds the size of the array and triggers the exception that you're seeing.
Since the array is supposed to be populated by inorderTraverse(), this suggests that that function isn't doing its job correctly. The reason why it is misbehaving is that its inner recursive calls to itself do not modify the value of the count variable for the caller. count is a simple int variable, therefore the count++ statement inside the recursive call does not affect the value of count in the calling function.
Your best options are either to change inorderTraverse() so that it returns the index of the array element that should be filled in next, or change count to be an Object that contains an int member whose updated value will be visible to the caller after it has been incremented inside the recursively called function.
Since this is an assignment I'm not going to show a corrected version of the program. The change is small, so given what you've done so far I expect that you won't have much trouble making it work.
BTW, your program is missing implementations of printIn(), printPre() and printPost(). They're not hard to write, but it's an extra hurdle for anyone who might have been interested in helping you tackle the problem. That might be at least part of the reason why no-one else has offered an answer yet. The easier you make it for people to reproduce the problem, the more likely it is that you'll get answers.
I made a postfix calculator and I'm pretty sure it works however it as a reading error. The calculator is designed to read numbers in postfix notation from a line in a file and calc them. However it doesn't recognize lines, for example if I have two lines it will combine the two expressions. I have trouble with file reading so any help would be appreciated. Sorry for any format problem this is my first post. So here is my code so my issue is better understood.
import java.io.*;
import java.util.*;
import java.nio.charset.Charset;
public class PostfixCalculator {
private static final String ADD = "+";
private static final String SUB = "-";
private static final String MUL = "*";
private static final String DIV = "/";
private static final String EXP = "^";
private static final String NEG = "_"; //unary negation
private static final String SQRT = "#";
public void calculateFile(String fileName) throws IOException {
BufferedReader br = null;
StringBuilder sb = null;
try {
FileReader fileReader = new FileReader(fileName);
br = new BufferedReader(fileReader);
sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
line = br.readLine();
}
String input = sb.toString();
System.out.println(input + " = " + calculate(input));
} catch (IOException e) {
e.printStackTrace();
} finally {
br.close();
}
}
private double calculate(String input) {
SinglyLinkedListStack<Double> stack = new SinglyLinkedListStack<Double>();
String[] inputs = input.split(" ");
return handleCalculation(stack, inputs);
}
private static double handleCalculation(SinglyLinkedListStack<Double> stack, String[] el) {
double operand1, operand2;
for(int i = 0; i < el.length; i++) {
if( el[i].equals(ADD) || el[i].equals(SUB) || el[i].equals(MUL) || el[i].equals(DIV)||el[i].equals(EXP)||el[i].equals(NEG)||el[i].equals(SQRT)) {
operand2 = stack.pop();
operand1 = stack.pop();
switch(el[i]) {
case ADD: {
double local = operand1 + operand2;
stack.push(local);
break;
}
case SUB: {
double local = operand1 - operand2;
stack.push(local);
break;
}
case MUL: {
double local = operand1 * operand2;
stack.push(local);
break;
}
case DIV: {
double local = operand1 / operand2;
stack.push(local);
break;
}
case EXP: {
double local = Math.pow(operand1, operand2);
stack.push(local);
break;
}
case NEG: {
double local = -(operand1);
stack.push(local);
break;
}
case SQRT:{
double local = Math.pow(operand1, .5);
stack.push(local);
break;
}
}
} else {
stack.push(Double.parseDouble(el[i]));
}
}
return (double)stack.pop();
}
}
This is my linked list
public class SinglyLinkedListStack<T> {
private int size;
private Node<T> head;
public SinglyLinkedListStack() {
head = null;
size = 0;
}
public void push(double local) {
if(head == null) {
head = new Node(local);
} else {
Node<T> newNode = new Node(local);
newNode.next = head;
head = newNode;
}
size++;
}
public T pop() {
if(head == null)
return null;
else {
T topData = head.data;
head = head.next;
size--;
return topData;
}
}
public T top() {
if(head != null)
return head.data;
else
return null;
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
private class Node<T> {
private T data;
private Node<T> next;
public Node(T data) {
this.data = data;
}
}
}
This is my demo
import java.io.IOException;
public class PostFixCalculatorDemo {
public static void main(String[] args) throws IOException {
PostfixCalculator calc = new PostfixCalculator();
calc.calculateFile("in.dat");
}
}
The text file contains
2 3 ^ 35 5 / -
1 2 + 3 * # 4 - 5 6 - + _
my output is 2 3 ^ 35 5 / -1 2 + 3 * # 4 - 5 6 - + _ = -8.0
as it is seen it is combining the two lines. I want it to read the two lines separately and calculate 2 3 ^ 35 5 / - and 1 2 + 3 * # 4 - 5 6 - + _ without putting it together. I know it does this because I programmed the calculateFile class wrong but I am not sure how to fix this without breaking my program.
while (line != null) {
sb.append(line);
line = br.readLine();
}
Basically you are reading every line and appending it to a single Stringbuffer which will result in concatenation of every line from your file. This buffer wont contain newline character or any other sign where your lines end.
From the documentation:
readline:
Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.
Returns: A String containing the contents of the line, not including
any line-termination characters, or null if the end of the stream has
been reached Throws:
I advice adding the lines to an ArrayList if you are planning to read everything at once.
I am finishing up an expression tree program that takes in a postfix and gives the answer and the orginal equation back in infix form. I started working on about 6 months ago and had an issue I couldn't figure out. It works fine if the numbers are smaller than 9. For instance, 2 5 * 4 - prints out The infix: (2*5-4) 6.0 works fine. Something like 10 2 * prints out 20.0 but prints out The infix: (0*2) which isn't right. The big problem is that if a number is bigger than 9 it doesn't read that number in properly which messes up the conversion to infix. I am not sure how to fix this problem exactly. Below is my class and tester class:
import java.util.NoSuchElementException;
import java.util.Stack;
public class ExpressionTree
{
private final String postfix;
private TreeNode root;
/**
* Takes in a valid postfix expression and its used to construct the expression tree.
*/
public ExpressionTree(String postfix)
{
if (postfix == null) { throw new NullPointerException("The posfix should not be null"); }
if (postfix.length() == 0) { throw new IllegalArgumentException("The postfix should not be empty"); }
this.postfix = postfix;
}
private static class TreeNode
{
TreeNode left;
char ch;
TreeNode right;
TreeNode(TreeNode left, char ch, TreeNode right) {
this.left = left;
this.ch = ch;
this.right = right;
}
}
/**
* Checks to see if it is an Operator
*/
private boolean isOperator(char c) {
return c == '+' || c == '-' || c == '*' || c == '/';
}
/**
* Constructs an expression tree, using the postfix expression
*/
public void createExpressionTree()
{
final Stack<TreeNode> nodes = new Stack<TreeNode>();
for (int i = 0; i < postfix.length(); i++)
{
char ch = postfix.charAt(i);
if (isOperator(ch))
{
TreeNode rightNode = nodes.pop();
TreeNode leftNode = nodes.pop();
nodes.push(new TreeNode(leftNode, ch, rightNode));
}
else if (!Character.isWhitespace(ch))
{
nodes.add(new TreeNode(null, ch, null));
}
}
root = nodes.pop();
}
/**
* Returns the infix expression
*
* #return the string of infix.
*/
public String infix()
{
if (root == null)
{
throw new NoSuchElementException("The root is empty, the tree has not yet been constructed.");
}
final StringBuilder infix = new StringBuilder();
inOrder(root, infix);
return infix.toString();
}
private void inOrder(TreeNode node, StringBuilder infix)
{
if (node != null) {
inOrder(node.left, infix);
infix.append(node.ch);
inOrder(node.right, infix);
}
}
public Double evaluate(String postfix)
{
Stack<Double> s = new Stack<Double>();
char[] chars = postfix.toCharArray();
int N = chars.length;
for(int i = 0; i < N; i++)
{
char ch = chars[i];
if(isOperator(ch))
{
switch(ch)
{
case '+': s.push(s.pop() + s.pop()); break;
case '*': s.push(s.pop() * s.pop()); break;
case '-': s.push(-s.pop() + s.pop()); break;
case '/': s.push(1 / s.pop() * s.pop()); break;
}
}
else if(Character.isDigit(ch))
{
s.push(0.0);
while (Character.isDigit(chars[i]))
s.push(10.0 * s.pop() + (chars[i++] - '0'));
}
}
return s.pop();
}
}
And the tester:
import java.util.Scanner;
public class ExpressionTester
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
String line = null;
while(true)
{
System.out.println("");
String pf = sc.nextLine();
if (pf.isEmpty())
{
break;
}
ExpressionTree eT = new ExpressionTree(pf);
eT.createExpressionTree();
System.out.println("The infix: " + "(" + eT.infix() + ")" );
System.out.println(eT.evaluate(pf));
}
}
}
I have a string array that looks like this:
[67, +, 12, -, 45]
I want to print it out so that it looks like this:
67 12 + 45 -
Here's the code I'm trying to use to do this.
String[] temp = line.split(" ");
String tmp = line.replaceAll("\\s+","");
for(int i = 0; i < temp.length; i++)
{
if(isInt(temp[i]) == false)
{
expression = temp[i];
firstExp = true;
}
else if(isInt(temp[i]) == false && firstExp == true && secondExp == false)
{
System.out.print(expression);
secondExp = true;
}
else if(isInt(temp[i]) == false && firstExp == true && secondExp == true)
{
System.out.print(expression);
firstExp = false;
secondExp = false;
}
else
{
System.out.print(temp[i]);
}
}
firstExp and secondExp are Booleans that check for the expressions that should appear in the array. isInt() is just a method used to determine if the string is a number. Right now, all this code does is output this:
671245
public static void main (String[] args) throws java.lang.Exception
{
String[] expr = new String[]{"67", "+", "45", "-", "12", "*", "5", "/", "78"};
int current = 0;
StringBuilder postfix = new StringBuilder();
// handle first three
postfix.append(expr[current]).append(" ");
postfix.append(expr[current+2]).append(" ");
postfix.append(expr[current+1]).append(" ");
current += 3;
// handle rest
while( current <= expr.length-2 ){
postfix.append(expr[current+1]).append(" ");
postfix.append(expr[current]).append(" ");
current += 2;
}
System.out.println(postfix.toString());
}
Outputs:
67 45 + 12 - 5 * 78 /
You can run/edit this at: http://ideone.com/zcdlEq
I guess what you are trying to do is converting infix expression to post fix. Some time back I had written the following code:
public class InfixToPostfix {
private Stack stack;
private String input;
private String output = "";
public InfixToPostfix(String in) {
input = in;
int stackSize = input.length();
stack = new Stack(stackSize);
}
public String translate() {
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case '+':
case '-':
hastOperator(ch, 1);
break;
case '*':
case '/':
hastOperator(ch, 2);
break;
case '(':
stack.push(ch);
break;
case ')':
hasSuperior(ch);
break;
default:
output = output + ch;
break;
}
}
while (!stack.isEmpty()) {
output = output + stack.pop();
}
System.out.println(output);
return output;
}
public void hastOperator(char op, int precedence) {
while (!stack.isEmpty()) {
char opTop = stack.pop();
if (opTop == '(') {
stack.push(opTop);
break;
}
else {
int prec2;
if (opTop == '+' || opTop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < precedence) {
stack.push(opTop);
break;
}
else
output = output + opTop;
}
}
stack.push(op);
}
public void hasSuperior(char ch){
while (!stack.isEmpty()) {
char chx = stack.pop();
if (chx == '(')
break;
else
output = output + chx;
}
}
public static void main(String[] args)
throws IOException {
String input = "67 + 12 - 45";
String output;
InfixToPostfix theTrans = new InfixToPostfix(input);
output = theTrans.translate();
System.out.println("Postfix is " + output + '\n');
}
class Stack {
private int maxSize;
private char[] stackArray;
private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
}
}
You may need to modify this program to read from an array, but that is very trivial.
Here's how you do it in one line:
System.out.println(Arrays.toString(temp).replaceAll("[^\\d +*/-]", "").replaceAll("[+*/-]) (\\d+)", "$2 $1"));