Question

Why do we need a dynamic stack and How to implement a dynamic array stack? ( Please answer in Java)

Answer 1

A stack stores elements in an ordered list and allows insertions and deletions at one end of the list in O(1) time. The dynamic stack array implements a stack using an array. The size of the array may be changed dynamically after insertions or deletions. For run-time requirements, the number of elements in the stack is n.

Example in Java:

public class DynamicArrayStack {
    public static void main(String[] args) {

        DynamicStack dstack=new DynamicStack(2);
        System.out.println("--Pushing--");
        dstack.push(1);
        dstack.push(2);
        dstack.display();
        dstack.push(3);
        dstack.push(2);
        dstack.push(5);
        dstack.display();
        System.out.println("--Popping--");
        dstack.pop();
        dstack.pop();
        dstack.pop();
        dstack.display();

    }

}

class DynamicStack {
    private int top;
    private int capacity;
    private int[] array;

    public DynamicStack(int cap) {
        capacity = cap;
        array = new int[capacity];
        top = -1;
    }

    public void push(int data) {
        if (isFull()){
            expandArray();      //if array is full then increase its capacity
        }
        array[++top] = data;    //insert the data
    }

    public void expandArray() {
        int curr_size = top + 1;
        int[] new_array = new int[curr_size * 2];
        for(int i=0;i<curr_size;i++){
            new_array[i] = array[i];
        }
        array = new_array;              //refer to the new array 
        capacity = new_array.length;
    }

    public boolean isFull() {
        if (capacity == top+1)
            return true;
        else
            return false;
    }

    public int pop() {
        if (isEmpty()) {
            System.out.println("Stack is empty");
            return -1;
        } else {
            reduceSize();                 //function to check if size can be reduced
            return array[top--];
        }
    }

    public void reduceSize() {
        int curr_length = top+1;
        if (curr_length < capacity / 2) {
            int[] new_array = new int[capacity / 2];
            System.arraycopy(array, 0, new_array, 0, new_array.length);
            array = new_array;
            capacity = new_array.length;
        }
    }

    public boolean isEmpty() {
        if (top == -1)
            return true;
        else
            return false;
    }

    public void display() {
        for (int i = 0; i <= top; i++) {
            System.out.print(array[i] + "=>");
        }
        System.out.println();
        System.out.println("ARRAY SIZE:" + array.length);
    }

}

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The code above shows pushing and poping in java language in dynamiv array stack.

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