Stack Array Algorithm
The Stack Array Algorithm is a fundamental data structure algorithm that simulates a linear, LIFO (Last In First Out) collection of elements. This algorithm is based on the concept of a stack, where elements are added and removed from a single end, called the top of the stack. Due to its simplicity and ease of implementation, it is widely used in computer programming for various applications such as memory management, parsing expressions, and function call management.
The Stack Array Algorithm typically consists of two primary operations: push and pop. The push operation adds an element to the top of the stack, while the pop operation removes the topmost element from the stack. Additionally, there are auxiliary operations like peek (which returns the top element without removing it) and is_empty (which checks if the stack is empty). Implementing this algorithm using an array involves managing an index to keep track of the top of the stack. When an element is pushed onto the stack, the index is incremented, and the element is stored in the corresponding position in the array. Similarly, when an element is popped, the index is decremented, and the element is retrieved from the array. This simple yet efficient algorithm has proven to be invaluable in various aspects of computer programming and is a foundational concept in computer science.
package DataStructures.Stacks;
/**
* This class implements a Stack using a regular array.
* <p>
* A stack is exactly what it sounds like. An element gets added to the top of
* the stack and only the element on the top may be removed. This is an example
* of an array implementation of a Stack. So an element can only be added/removed
* from the end of the array. In theory stack have no fixed size, but with an
* array implementation it does.
*
* @author Unknown
*/
public class StackArray {
/**
* Main method
*
* @param args Command line arguments
*/
public static void main(String[] args) {
// Declare a stack of maximum size 4
StackArray myStackArray = new StackArray(4);
// Populate the stack
myStackArray.push(5);
myStackArray.push(8);
myStackArray.push(2);
myStackArray.push(9);
System.out.println("*********************Stack Array Implementation*********************");
System.out.println(myStackArray.isEmpty()); // will print false
System.out.println(myStackArray.isFull()); // will print true
System.out.println(myStackArray.peek()); // will print 9
System.out.println(myStackArray.pop()); // will print 9
System.out.println(myStackArray.peek()); // will print 2
}
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* The max size of the Stack
*/
private int maxSize;
/**
* The array representation of the Stack
*/
private int[] stackArray;
/**
* The top of the stack
*/
private int top;
/**
* init Stack with DEFAULT_CAPACITY
*/
public StackArray() {
this(DEFAULT_CAPACITY);
}
/**
* Constructor
*
* @param size Size of the Stack
*/
public StackArray(int size) {
maxSize = size;
stackArray = new int[maxSize];
top = -1;
}
/**
* Adds an element to the top of the stack
*
* @param value The element added
*/
public void push(int value) {
if (!isFull()) { // Checks for a full stack
top++;
stackArray[top] = value;
} else {
resize(maxSize * 2);
push(value); // don't forget push after resizing
}
}
/**
* Removes the top element of the stack and returns the value you've removed
*
* @return value popped off the Stack
*/
public int pop() {
if (!isEmpty()) { // Checks for an empty stack
return stackArray[top--];
}
if (top < maxSize / 4) {
resize(maxSize / 2);
return pop();// don't forget pop after resizing
} else {
System.out.println("The stack is already empty");
return -1;
}
}
/**
* Returns the element at the top of the stack
*
* @return element at the top of the stack
*/
public int peek() {
if (!isEmpty()) { // Checks for an empty stack
return stackArray[top];
} else {
System.out.println("The stack is empty, cant peek");
return -1;
}
}
private void resize(int newSize) {
int[] transferArray = new int[newSize];
for (int i = 0; i < stackArray.length; i++) {
transferArray[i] = stackArray[i];
}
// This reference change might be nice in here
stackArray = transferArray;
maxSize = newSize;
}
/**
* Returns true if the stack is empty
*
* @return true if the stack is empty
*/
public boolean isEmpty() {
return (top == -1);
}
/**
* Returns true if the stack is full
*
* @return true if the stack is full
*/
public boolean isFull() {
return (top + 1 == maxSize);
}
/**
* Deletes everything in the Stack
* <p>
* Doesn't delete elements in the array
* but if you call push method after calling
* makeEmpty it will overwrite previous
* values
*/
public void makeEmpty() { // Doesn't delete elements in the array but if you call
top = -1; // push method after calling makeEmpty it will overwrite previous values
}
}
