The following program is a recursive program to check for repeated entries in an array. The program compiles with no errors, however after i input the command-line arguments and hit enter, it doesn't proceed. The cursor just blinks! It doesn't return any Runtime errors too! If someone explains why this is happening, it'd be very helpful! Thanks! :)
import java.io.*;
class RepeatEntries_Recursive
{
static int i=0,flag=0;
public static void main(String[] args) throws IOException
{
int[] inp = new int[6];
for(int k=0;k<args.length;k++)
inp[k] = Integer.parseInt(args[k]);
boolean hasItRepeated = Repeating(inp,i);
if(hasItRepeated == true)
System.out.println("\nYes, there are entries that repeat in the array!");
else
System.out.println("\nNo, entries don't repeat in the array");
}
static boolean Repeating(int[] inp,int i)
{
for(int j=0;j<inp.length;j++)
{
if(inp[i] == inp[j])
flag = 1;
while(i<inp.length-1)
Repeating(inp,i+1);
}
if(flag==1)
return true;
else
return false;
}
}
while(i<inp.length-1)
Repeating(inp,i+1);
Your program can't ever escape from this loop.
Related
I am writing a stack data structure in java using arrays. The problem is when I try to push the users char input it doesn't display. The problem is with this code.
public static void preSuf(Stack stack) {
Scanner key = new Scanner(System.in);
System.out.println("enter the values");
while(key.hasNext()){
char c = key.next().charAt(0);
stack.push(c);
}
}
When I change the while(key.hasNext()) to if(key.hasNext()) it works but it only prints one time and doesnt itterate. How can I fix this problem thank you.
Edit: Here is the whole code
import java.util.Scanner;
public class Stack {
private int top;
private char[] container;
private int size;
public static int pos = 0;
// constructor
public Stack(int N) {
container = new char[N];
size = N;
top = 0;
}
public boolean isFull() {
return (size == top);
}
public void push(char string) {
if (!isFull()) {
container[top] = string;
top++;
} else {
return;
}
}
public int pop() {
int drop;
drop = container[top - 1];
container[top] = 0;
top--;
return drop;
}
public int peek() {
int drop2;
drop2 = container[top - 1];
return drop2;
}
public void display() {
for (int i = 0; i < container.length; i++) {
if (container[i] != 0) {
System.out.print(container[i]);
}
}
}
public static void preSuf(Stack stack) {
Scanner key = new Scanner(System.in);
System.out.println("enter the values");
while(key.hasNext()){
char c = key.next().charAt(0);
stack.push(c);
}
}
public static void main(String args[]) {
Stack stack = new Stack(3);
preSuf(stack);
stack.display();
stack.display();
System.out.println();
}
}
The problem is that you haven't written any code to actually print the contents of your stack.
You could write a loop after your while loop to iterate over the stack and print out each character.
You'll also need a way of exiting your while loop. You can do this either with a special character, eg. if(c == '.') break; or you can just press Ctrl+Z.
EDIT: Based on the edit to the question and the full code being presented, I think the suggestion of needing the extra loop is now redundant. You have that in stack.display(). You just need to get out of your while loop.
you haven't determined when the loop should end.
you'd think if you press enter without entering anything the loop
would break but that's not how next operates. if you press enter
without entering anything or input data which consists of only whitespaces, next will block while waiting for input to
scan, even if a previous invocation of hasNext() returned true.
the solution is to include a condition at which control should break out of the loop.
Given a string S and Q queries, each query contains a string T. The task is print “Yes” if T is subsequence of S, else print “No”.
I am trying to learn algorithms and implementing them.
I have written the below code in Java :
import java.util.Stack;
public class QueriesOnStringSubsequence {
public boolean subSequence(String original, String query) {
Stack<Character> s1 = new Stack<Character>();
Stack<Character> s2 = new Stack<Character>();
for (int i = 0; i < original.length(); i++) {
s1.push(original.charAt(i));
System.out.println(s1.peek());
}
for (int i = 0; i < query.length(); i++) {
s2.push(query.charAt(i));
System.out.println(s2.peek());
}
while (!s1.isEmpty() || !s2.isEmpty()) {
Character s1Top = s1.peek();
Character s2Top = s2.peek();
if (s1Top == s2Top) {
s1.pop();
//System.out.println(i);
s2.pop();
return true;
}
System.out.print("True");
}
System.out.print("False");
return false;
}
public static void main(String[] args) {
QueriesOnStringSubsequence ob = new QueriesOnStringSubsequence();
ob.subSequence("geeksforgeeks", "gg");
}
}
I tried to debug this and in Eclipse and it won't go into the if condition. Can someone please explain where I am going wrong.
Keep in mind that Stack are LIFO data structures.
This means when you run:
Character s1Top = s1.peek();
Character s2Top = s2.peek();
You are getting the last two characters added. In this case s and g.
This means that the if statement will not be met. The second time the software loops since you are using Stack.peek the element is looked at but not changed. Therefore your while loop is looking at s and g over and over. Since they are never equal your if will never be met and therefore your while loop will be infinite.
Also you are checking:
while(!s1.isEmpty() || !s2.isEmpty())
This means both need to be empty before exiting which can cause an issue. I believe you want to use:
while(!s1.isEmpty() && !s2.isEmpty())
As duncan pointed out, a stack may not be the best data structure for this. I assume you want to go in order which means that you should use a queue.
Here is an implementation. I used better variable naming conventions which help not only in readability, but also debugging.
import java.util.*;
public class QueriesOnStringSubsequence {
public static void subSequence(String original, String query) {
Queue<Character> originalQueue = stringToQueue(original);
Queue<Character> queryQueue = stringToQueue(query);
while (!originalQueue.isEmpty() && !queryQueue.isEmpty()) {
Character originalQueueHead = originalQueue.peek();
Character queryQueueHead = queryQueue.peek();
if (originalQueueHead.equals(queryQueueHead)) {
queryQueue.poll();
System.out.print("YES");
} else {
System.out.print("NO");
}
originalQueue.poll();
System.out.print("...");
}
}
private static Queue<Character> stringToQueue(String input) {
Queue<Character> queue = new LinkedList<Character>();
for (int i = 0; i < input.length(); i++) {
queue.add(input.charAt(i));
}
return queue;
}
public static void main(String[] args) {
QueriesOnStringSubsequence.subSequence("geeksforgeeks", "gg");
}
}
YES...NO...NO...NO...NO...NO...NO...NO...YES...
I am doing a pretty simple program, where a user will be prompted to enter up to 80 characters. We need to build our own stack and push each character onto the stack. Then pop and display the characters in reversed order. Thought I was done, but my instructor wants me to do something if a user enters more than 80 characters. Basically, I need to ignore all characters over 80. How would I go about doing this? I have been trying to figure this out, but can't get it. I am sure it will be something simple that I completely missed. Any help, suggestions, are appreciated!
stackUser
import java.util.Scanner;
public class stackUser {
public static void main(String[] args){
System.out.println("\nPlease enter up to 80 characters and I will reverse them: ");
Scanner key = new Scanner(System.in);
String input = key.nextLine();
myStack stack = new myStack();
for(int i = 0; i < input.length(); i++){
char c = input.charAt(i);
stack.push(c);
}
if(stack.isEmpty()){
System.out.println("Stack is empty!");
}else{
while(!stack.isEmpty()){
char rev = stack.pop();
System.out.print(rev);
}
}
}
}
myStack
public class myStack {
private int max = 80;
private char[] Stack = new char[max];
private int top = -1;
public void push(char input){
top++;
Stack[top] = input;
}
public char pop(){
char popped = Stack[top];
top --;
return popped;
}
public boolean isEmpty(){
boolean empty;
if(top == -1){
empty = true;
}else{
empty = false;
}
return empty;
}
}
Handle ArrayIndexOutOfBoundsException is bad idea, you need to check current top value with max value. Because ArrayIndexOutOfBoundsException is unchecked exception, and it means that error of developer.
I would declare the push method like this to indicate that it will throw an exception if the max is reached:
public void push(char input) throws ArrayIndexOutOfBoundsException{
top++;
Stack[top] = input;
}
Then in the main method you can use a try/catch block to handle the exception:
try{
stack.push(c);
}catch (ArrayIndexOutOfBoundsException ex){
System.out.println("too much!");
}
A try catch loop around anything that will throw an IndexOutOfBounds
try {
...code here
}
catch (ArrayIndexOutOfBoundsException e) {
...whatever you want to do in event of exception
}
I can't seem to get the "The numbers match" result if my input is a number that is in my array list in another class called SomeNumbers. If you run it, it will give you the result for it not being a number in the array at the speed of light though.
I am also having a hard time pin pointing where the actual problem is because I can use my debugging tools for whatever reason in jGrasp.
This is the main application that the user would input the number to see if there is a match.
import java.util.Scanner;
public class SomeNumbersClient {
public static void main(String[] args) {
SomeNumbers testNumbers = new SomeNumbers();
Scanner userInput = new Scanner(System.in);
System.out.print("Enter Integer Value: ");
int input = userInput.nextInt();
testNumbers.setNumber(input);
if (testNumbers.getTest()) {
System.out.println("The numbers match");
} else {
System.out.println("The numbers don't match");
}
}
}
Now this is the class where I call on the getTest method to see if the boolean result is true or false. I then have the if statement in the client see if it's true then it will display that there is a match, if not, there is no match.
public class SomeNumbers {
private int[] numbers = { 5658845, 4520125, 7895122, 8777541, 8451277, 1302850, 8080152, 4562555, 5552012, 5050552, 7825877, 120255, 1005231, 6545231, 3852082, 7576651,7881200, 4581002};
private int number;
private int index = 0;
private boolean test = true;
public void setNumber(int input) {
number = input;
}
public boolean getTest(){
while (index < numbers.length){
if (number != numbers[index]){
test = false;
index++;
} else {
test = true;
}
}
return test;
}
}
Sorry the code kind of got chopped up, any help is appreciated.
here is proper version of getTest function, your problem was because you find match (and set variable test to true), but then you continue search and next number converts "test" to false
public boolean getTest()
{
index = 0;
while (index < numbers.length)
if (number != numbers[index])
index++;
else
return true;
return false;
}
I'm working on a project for school and am stumped at where I am at the moment. When I run my project, the VM seems to be stuck in a loop and will not load (A console should pop up allowing me to input characters for the CombinationLock class setDigit() method). I believe it has something to do with my for loop in my Interface.java class. If anyone could take a look and lead me in the right direction, that'd be much appreciated. Thanks a bunch!
Interface.java
import java.util.*;
public class Interface
{
public static void main() {
Scanner in = new Scanner(System.in);
CombinationLock combo = new CombinationLock();
for(int i = 0; i < 3; i++) {
String ltr = in.nextLine();
combo.setDigit(ltr.charAt(0), i);
System.out.println("Digit " + i + " has been set to " + ltr);
}
}
}
CombinationLock.java
public class CombinationLock
{
String[] combo = new String[3];
public CombinationLock() { }
public boolean setDigit(char letter, int index) {
if (Character.isDigit(letter)) {
return false;
}
combo[index] = String.valueOf(letter);
return true;
}
public boolean unlock(String combo) {
if (combo.length() > 3) {
return false; //Longer then it can be, not valid
}
char[] comboArray = combo.toCharArray();
for (char c : comboArray) {
if (Character.isDigit(c)) {
return false; //Contains numbers, not valid
}
}
boolean valid = true;
for (int i = 0; i < 3; i++) {
if (combo.charAt(i) != comboArray[i] && valid == true) {
valid = false;
break;
}
}
return valid;
}
}
You have initialized combo array in CombinationLock class with length 0 as String[] combo = {};. This is cause ArrayIndexOutOfBoundsException when you are calling combo.setDigit(ltr.charAt(0), i);. Please correct the initialization. I beleive you want to capture 3 inputs, in that case, please initialize combo in CombinationLock with length 3 as below:
String[] combo = new String[3];
Your problem is (the signature of the main method is wrong)
public static void main() {
it should be
public static void main(String[] args) {
I've found where my error was, using the BlueJ IDE one must output something to the console before it shows up and allows you to input data, therefore it never popped up as I never used System.out.println or System.out.print. After doing so, the console popped up and allowed me to input my data. Thanks you for all your suggestions and help!