Javascript Priority Queue

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How to use PriorityQueue in Java

Priority queues are used in programming to create data structures where the data item with the highest value must be processed first by the structure.

coding in Java, you may come across a situation where you want to implement priority queue. This is where the Java Queue interface comes in. However, because the queue is an interface, it cannot be implemented directly in code. If you want to create a priority queue with the heaped data structure, you will need to use PriorityQueue instead.

This tutorial will discuss the basics of PriorityQueue in Java and explore how to create a queue . This tutorial will also explore the main methods offered by PriorityQueue that can be used to retrieve and manipulate the content of the queue .

Java code and PriorityQueue

Queues, like stacks, are given structures that have a specific order in which operations are performed. In the case of queues , operations are performed for First In, First Out (FIFO). This means that the first item on the list will always be the first to come out - . The queue is sorted by the items entered

Suppose you are in a restaurant and you have placed an order. We recommend that you be served the moment each customer has ordered their food, because that is the nicest approach. So if you ordered your food after Jack, you want to be served immediately after Jack. This is an example of a queue .

For the purposes of this tutorial, we will focus on developing work PriorityQueue the interface queue, waiting, which is used to create lines of priority queue in Java.

PriorityQueues are a type of queue i whose items are sorted according to their priority. This means that in a queue with values ‚Äã‚Äã5 and 10, 10 will always be at the top of the queue , even if it was added last.

Create priority queue

To create priority queue in Java, you must first import the java.util.PriorityQueue . This package contains the PriorityQueue method which we can use to create our queues . We can import the PriorityQueue package using this code:

now, we imported PriorityQueue, we can create a queue of waiting in using the package. the syntax used to create a PriorityQueue:

FIND Let this:

  • PriorityQueue tells our program it wants to create a priority queue
  • DataType is the type of data to our queue, waiting to store.
  • queue_name is the name of the variable to which the queue of waiting, we create will be. awarded
  • new PriorityQueue (); initialize a priori queue shut up

So suppose we want to create a queue that stores customer orders in our restaurant we want our queue to store each customer’s table number we could create this stack using the following code: ..

In this example we have created a PriorityQueue instance called orders integer values ‚Äã‚Äã which stores. in our queue , items will be accessed and deleted using the FIFO data structure.

Add element to PriorityQueue

In Java, each element in a queue is called element.

to add an item to a queue , we can use the add () This method takes one parameter: va lore of the item you want to add to your queue . If the queue of waiting e is full, the add () returns an exception.

Additionally , we can use the Offer () to add an item to a queue. The difference between add () and Offer () is that Offer () returns false if the queue is full, while add () throws an exception.

Suppose we want to add tables # 22 and # 17 in that order to our stack because they just ordered lunch. We could do it using this code:

Our code returns:

Break from Descended our example. First, we imported the PriorityQueue class, which we will use later in our code. So, we’ve declared a class called AddCustomer, which stores our code for this example. This is how the code in our class works:

  1. We use new PriorityQueue <> (); to create a priority queue called commands.
  2. We use add () to add table # 22 to our stack
  3. We print the word commands:. followed by the contents of our stack at the console.
  4. We use offer () to add table # 17 to our stack.
  5. We print to the console the term updated commands . followed by the revised contents of our stack
  6. 22 appears first in our stack, and will thus be the first to exit when we remove an element. In other words, array # 22 is at the top of our stack. Table # 17 is stored in the second position in our stack. Remember - you, the queues of priority waiting are classified in the FIFO order

Our code returns an array with our original commands, then an array with our updated commands .

remove item from PriorityQueue

There are two methods that can be used to remove an item from a PriorityQueue:

Suppose our sub-boss has processed command # 17 and wants to remove it from the stack. After the order was processed, our chef prepared for no. 22 and wants to remove from the stack.

Ref. 17 is in position 2 of our stack and order no. 22 is in position 1. We want to eliminate these items in that order. We could use this code to remove the commands:

Our code returns:

Let our code pause. First, we used the delete () to delete the order at position 2 in our stack. This command # 17 deleted

our code printed a message saying:.? Order # 17 was deleted followed by the result of delete () method. delete () successfully removed # 17 from our stack, the method returns true

Next, we used poll () to remove the top item from our stack. In this case it was no order. 22. poll () has the order deleted ne. 22 and returned the deleted item. After the item was removed, we printed the message Commander # [order number removed] has been removed from the queue . in the console.

Get Item

The peek () method is used to retrieve the header of a queue item (the first item in the queue ). Suppose we want to know the value of the next order in our stack because our sous chef is ready to accept a new order.

We could use this code to retrieve the table number of the client which is next to the line:

Our code returns:

the first element in our stack is 22, so when we use the peek (), our program returns the value 22 "last row of our code, we print a message that says:. the order to be processed is table # [first order number on stack], where the first order number on the stack was discovered by peek ().

Queue iterates by priority

Often when working with queues you want to iterate over the items in the priority queue


To do this we can use the iterator (), which is part of the java.util.Iterator package.we use the code <> iterator () , you must first import the Iterator package using this code:

Suppose we want to print a list of all the items in our restaurant order queue to the console we could do using this code:.

Our code returns:

In our code, we first add four values ‚Äã‚Äãto our queue . We then use the iterator () to create an iterator that we can use to examine all of the items in our priority queue. Next, we create a while that goes through each element in our iterator - for each element in the command queue - . And prints the following value in the queue <

h2> additional methods PriorityQueue

There are three other methods that are often used with the PriorityQueue class. These are:

Name of the method description
size () returns the length of the queue .
toArray () converts queue to an array.
contains (elementName) Search the queue for an element.


PriorityQueue class is used in Java to implement the queue interface waiting. Queues use the FIFO data structure, so first is first out.

This tutorial showed the basics of Queuing and PriorityQueues in Java. We have also discussed how to create a queue and the main methods you can use to retrieve items and manipulate a queue .

Now you have the tools you need to start using the Java PriorityQueue class like a pro!


Javascript Priority Queue __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.


Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).


Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?


Answer #1

Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Javascript Priority Queue __delete__: Questions


Answer #2

Path objects from the Python 3.4+ pathlib module also expose these instance methods:


Answer #3

Python syntax to delete a file

import os


import os


pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")


Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

import os

## If file exists, delete it ##
if os.path.isfile(myfile):
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))


Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder


Example for shutil.rmtree()

import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

    b = a.index(6)
    del a[b]


But is there not a simpler way to do this?


Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]


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