Queues - Basic Practice Problems Online

The java code below is a simple implementation of an array based data structure that is either a stack or a queue. What type of structure is this, and how should the three methods one(), two(), and three() be renamed so that they describe their functions?

public class data_structure {
    private int limit = 1000000;
    private int[] arr = new int[limit];
    private int size = 0;
    private int rear = limit - 1;

    public void one(int element){
        arr[ rear ] = element;
        size ++;
        rear --;
    }

    public int two(){
        rear ++;
        int temp = arr[rear];
        arr[rear] = 0;
        size -= 1;
        return temp;
    }

    public int three(){
        return arr[rear + 1];
    }
}

Suppose the following operations are made on a circular queue structure.

Insert entry $A$ .
Insert entry $B$ .
Insert entry $C$ .
Remove an entry.
Remove an entry.
Insert entry $D$
Insert entry $E$ .
Remove an entry.
Insert entry $F$ .
Remove an entry.

After completing these operations, what are the remaining items in the queue?

The code below makes use of a deque object. A deque object is similar to a queue except that it allows the insertion/deletion of an element to both the back and front of the queue. What does the pseudocode below output?

function isTrue(string) //Defines a new function 'isTrue' that returns boolean
    deq = new Deque(); //Creates a new deque object
    for char in string{ 
        deq.addRear(char) 
    }

    boolean equal = true //Creates a boolean variable called true

    while (deq.size() > 1 and equal){
        first = deq.removeFront()
        last = deq.removeRear()
        if (first != last){
            equal = false
        }
    return equal

boolean value_a = isTrue("radar")
boolean value_b = isTrue("plus")
boolean value_c = isTrue("madam")

if (value_a and value_b and !value_c)
  print 1
else if (value_a and !value_b and value_c)
  print 2
else if (!value_a and value_b and value_c)
  print 3
else if (!value_a and !value_b and value_c)
  print 4
else if (!value_a and !value_b and !value_c)
  print 5
else
  print 6

The addRear(e) method adds an item to the rear of a deque,the addFront(e) to the front and removeFront() and removeRear() remove the front and rear items of a deque respectively.

Which of the following best represents a queue data structure?

A) A pile of dirty dishes requiring washing

B) Requests on a single shared resource, like a printer

C) A line of people waiting to go to an amusement park ride

D) (B) and (C)

The below is incomplete python code to implement a queue that uses only two int variables(self.size and self.val) to save its contents.

from math import log
class Integral_queue:   
    def __init__(self):
        self.val = 0
        self.size = 0

    def enqueue(self,value):
        self.val += value * pow(10,self.size)
        self.size += 1

        #def deque(self...) INCOMPLETE

    def peek(self):
        return self.val % 10

    def is_empty(self):
            return self.size == 0

However, this queue only supports single digit integers as elements. Specifically, the only elements that can be pushed to the queue are numbers in the range $1$ to $9$ . The dequeue() method of the queue class is incomplete. Which of the following methods correctly implements the dequeue() method?

A

def dequeue(self):
   power = pow(10,self.size-1)
   ret = self.val / power
   self.val = self.val % power
   self.size -= 1
   return ret

B

def dequeue(self):
   ret = self.val % 10
   self.val = self.val // 10
   self.size -= 1
   return ret

C

def dequeue(self):
  ret = floor(log(val,10))
  self.val /= 10
  size -= 1
  return ret

D

def dequeue(self):
  ret = int(str(self.val)[0])
  self.val = int(str(self.val)[1::])
  size -= 1
  return ret

Concept Quizzes

Challenge Quizzes

Queues - Basic

Abstract Data Types

Concept Quizzes

Challenge Quizzes

Queues - Basic