Stacks Using Array

A Stack is an ADT (abstract data type) that serves as a collection of elements, with two principal operations:

• push, which adds an element to the collection, and

• pop, which removes the most recently added element that was not yet removed

Algorithm

Push :

• Checks if the stack is full.
• If the stack is full, produces an error and exit.
• If the stack is not full, increments top to point next empty space.
• Adds data element to the stack location, where top is pointing.

Pop :

• Checks if the stack is empty.
• If the stack is empty, produces an error and exit.
• If the stack is not empty, accesses the data element at which top is pointing.
• Decreases the value of top by 1.

Pseudocodes

Structure of Stack

structure stack:
    maxsize : integer
    top : integer
    items : array of item

Push Operation

push( stk, x):
    if stk.top = stk.maxsize:
        report overflow error
    else:
        stk.items[stk.top] ← x
        stk.top ← stk.top + 1

Pop Operation

pop(stk):
    if stk.top = 0:
        report underflow error
    else:
        stk.top ← stk.top − 1
        r ← stk.items[stk.top]

Complexity

Time complexity

• Push : O(1)
• Pop : O(1)

Space complexity : O(n)

Implementation

• C++ Code

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• Java Code

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• Python Code

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