Stack data structure :
A stack is a linear data structure that follows the principle of Last in First out (LIFO). this means last element inserted inside the stack is removed first.
LIFO Principle of Stack :
In Programming Language, putting an item on top of the stack is called PUSH and removing on item is called POP.
In the above, Although item 2 was kept list it was removed first this is exactly how the LIFO Principle works.
Basic Operations of Stack :
PUSH : it is adding an element to the TOP of a Stack.
POP : it is Removing an element from the TOP of a Stack.
isEmpty : Check if the Stack is Empty.
isFull : Check if the Stack is Full.
Working of Stack DSA :
- A pointer known as prime is employed to stay track of the highest component within the stack.
- When initializing the stack, we have a tendency to set its worth to -1 in order that we are able to check if the stack is empty by TOP == -1.
- On pushing a part, we have a tendency to increase the worth of prime and place the new component within the position pointed to by prime.
- On sound a part, we have a tendency to come the component pointed to by prime and cut back its worth.
- Before pushing, we have a tendency to check if the stack is already full
- Before popping, we have a tendency to check if the stack is already empty
Stack Implementation using C, C++, JAVA, PYTHON:
Stack Implementation using C :
// Stack implementation in C
#include <stdio.h>
#include <stdlib.h>
#define MAX 10
int count = 0;
// Creating a stack
struct stack {
int items[MAX];
int top;
};
typedef struct stack st;
void createEmptyStack(st *s) {
s->top = -1;
}
// Check if the stack is full
int isfull(st *s) {
if (s->top == MAX - 1)
return 1;
else
return 0;
}
// Check if the stack is empty
int isempty(st *s) {
if (s->top == -1)
return 1;
else
return 0;
}
// Add elements into stack
void push(st *s, int newitem) {
if (isfull(s)) {
printf("STACK FULL");
} else {
s->top++;
s->items[s->top] = newitem;
}
count++;
}
// Remove element from stack
void pop(st *s) {
if (isempty(s)) {
printf("\n STACK EMPTY \n");
} else {
printf("Item popped= %d", s->items[s->top]);
s->top--;
}
count--;
printf("\n");
}
// Print elements of stack
void printStack(st *s) {
printf("Stack: ");
for (int i = 0; i < count; i++) {
printf("%d ", s->items[i]);
}
printf("\n");
}
// Driver code
int main() {
int ch;
st *s = (st *)malloc(sizeof(st));
createEmptyStack(s);
push(s, 1);
push(s, 2);
push(s, 3);
push(s, 4);
printStack(s);
pop(s);
printf("\nAfter popping out\n");
printStack(s);
}
Stack Implementation using C++ :
// Stack implementation in C++
#include <stdlib.h>
#include <iostream>
using namespace std;
#define MAX 10
int size = 0;
// Creating a stack
struct stack {
int items[MAX];
int top;
};
typedef struct stack st;
void createEmptyStack(st *s) {
s->top = -1;
}
// Check if the stack is full
int isfull(st *s) {
if (s->top == MAX - 1)
return 1;
else
return 0;
}
// Check if the stack is empty
int isempty(st *s) {
if (s->top == -1)
return 1;
else
return 0;
}
// Add elements into stack
void push(st *s, int newitem) {
if (isfull(s)) {
printf("STACK FULL");
} else {
s->top++;
s->items[s->top] = newitem;
}
size++;
}
// Remove element from stack
void pop(st *s) {
if (isempty(s)) {
printf("\n STACK EMPTY \n");
} else {
printf("Item popped= %d", s->items[s->top]);
s->top--;
}
size--;
cout << endl;
}
// Print elements of stack
void printStack(st *s) {
printf("Stack: ");
for (int i = 0; i < size; i++) {
cout << s->items[i] << " ";
}
cout << endl;
}
// Driver code
int main() {
int ch;
st *s = (st *)malloc(sizeof(st));
createEmptyStack(s);
push(s, 1);
push(s, 2);
push(s, 3);
push(s, 4);
printStack(s);
pop(s);
cout << "\nAfter popping out\n";
printStack(s);
}
Stack Implementation using JAVA :
// Stack implementation in Java
class Stack {
private int arr[];
private int top;
private int capacity;
// Creating a stack
Stack(int size) {
arr = new int[size];
capacity = size;
top = -1;
}
// Add elements into stack
public void push(int x) {
if (isFull()) {
System.out.println("OverFlow\nProgram Terminated\n");
System.exit(1);
}
System.out.println("Inserting " + x);
arr[++top] = x;
}
// Remove element from stack
public int pop() {
if (isEmpty()) {
System.out.println("STACK EMPTY");
System.exit(1);
}
return arr[top--];
}
// Utility function to return the size of the stack
public int size() {
return top + 1;
}
// Check if the stack is empty
public Boolean isEmpty() {
return top == -1;
}
// Check if the stack is full
public Boolean isFull() {
return top == capacity - 1;
}
public void printStack() {
for (int i = 0; i <= top; i++) {
System.out.println(arr[i]);
}
}
public static void main(String[] args) {
Stack stack = new Stack(5);
stack.push(1);
stack.push(2);
stack.push(3);
stack.push(4);
stack.pop();
System.out.println("\nAfter popping out");
stack.printStack();
}
}
Stack Implementation using PYTHON :
# Stack implementation in python
# Creating a stack
def create_stack():
stack = []
return stack
# Creating an empty stack
def check_empty(stack):
return len(stack) == 0
# Adding items into the stack
def push(stack, item):
stack.append(item)
print("pushed item: " + item)
# Removing an element from the stack
def pop(stack):
if (check_empty(stack)):
return "stack is empty"
return stack.pop()
stack = create_stack()
push(stack, str(1))
push(stack, str(2))
push(stack, str(3))
push(stack, str(4))
print("popped item: " + pop(stack))
print("stack after popping an element: " + str(stack))
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