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## Stacks And Queues

Last Updated: Nov 17, 2023
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Stacks And Queues
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# Queue Implementation Details

##### C :

Array / Linked list based implementation as shown in earlier lessons.

##### C++ :

C style array queue works in C++ as well. However, C++ provides a library implementation of queue as well.

###### Queue declaration : :
``````    queue<int> A; // declares an empty queue.
``````
###### Push
``````    A.push(newElement); // Pushes a new element. O(1)
``````
###### Pop
``````    A.pop(); // O(1) pop
``````
###### isEmpty
``````    A.empty() // O(1)
``````
###### Size
``````    A.size(); // O(1)
``````
###### Front
``````    A.front(); // O(1). Gives the first element.
``````
##### JAVA :

Java has a queue similar to C++.

###### Queue declaration : :
``````    Queue A = new LinkedList();
``````
###### Push
``````    A.add(new Integer(newElement)); // Pushes a new element. O(1)
``````
###### Pop
``````    A.poll(); // O(1) pop
``````
###### isEmpty
``````     A.isEmpty() // O(1)
``````
###### Size
``````    A.size(); // O(1)
``````
###### Front
``````    A.peek(); // O(1). Gives the top element.
``````
##### PYTHON :

We can use deque as a queue in python.

###### Queue declaration : :
``````    A = deque() # declares an empty queue. O(1)
``````
###### Push
``````    A.append(newElement) # Put the new Element on the end of the array. O(1).
``````
###### Pop
``````    A.popleft() # Pops out the front of the queue
``````
###### isEmpty
``````    return (len(A) == 0); # Check if size is 0. O(1)
``````
###### Size
``````    return len(A); # O(1)
``````
###### Front
``````    A[0] # O(1)
``````
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