ArrayStack.java

public class ArrayStack implements Stack {
    private int size;
    private Object[] a;

    public ArrayStack(int capacity) {
        a = new Object[capacity];
    }

    public boolean isEmpty() {
        return (size == 0);
    }

    public int size() {
        return size;
    }

    public Object peek() {
        if (size == 0) throw new IllegalStateException("Stack is empty");
        return a[size - 1];
    }

    public void push(Object obj) {
        if (size == a.length) {
            resize(); 
        }
        a[size++] = obj;
    }

    public Object pop() {
        if (size == 0) throw new IllegalStateException("Stack is empty");
        Object temp = a[--size];
        a[size] = null; // Memory free karne ke liye
        return temp;
    }

    private void resize() {
        Object[] aa = a;
        a = new Object[2 * aa.length];
        System.arraycopy(aa, 0, a, 0, size);
    }

    public Object getBottom() {
        if (size == 0) throw new IllegalStateException("Stack is empty");
        return a[0];
    }

    public Object getMiddle(){
        if (size == 0) throw new IllegalStateException("Stack is empty");
        int midIndex = size / 2;
        return a[midIndex];
    }

    public void reverse(){
        // if (size<=1){
        //     return;
        // }
        // int start = 0;
        // int end = size - 1;
        // while (start < end){
        //     Object temp = a[start];
        //     a[start] = a[end];
        //     a[end] = temp;
        //     start++;
        //     end--;
        // }
        // -----------------------------------------------
        if (size <= 1) {
            return; 
        }
        int originalSize = this.size;
        ArrayStack temp1 = new ArrayStack(this.a.length);
        while (this.size > 0) {
            temp1.push(this.pop());
        }
        System.arraycopy(temp1.a, 0, this.a, 0, originalSize);
        this.size = originalSize;
        // -----------------------------------------------
        // if (size <= 1) {
        //     return; 
        // }
        // ArrayStack temp1 = new ArrayStack(this.a.length);
        // ArrayStack temp2 = new ArrayStack(this.a.length);
        
        // while (this.size() > 0) {
        //     temp1.push(this.pop());
        // }
        // while (temp1.size() > 0) {
        //     temp2.push(temp1.pop());
        // }
        // while (temp2.size() > 0) {
        //     this.push(temp2.pop());
        // }

    }

    public int getmax(){
        if (size == 0) throw new IllegalStateException("Stack is empty");
        // ArrayStack tempStack = new ArrayStack(this.a.length);
        // int max = (int) this.pop();
        // tempStack.push(max);
        // while (this.size > 0){
        //     int current = (int) this.pop();
        //     if (current > max){
        //         max = current;
        //     }
        //     tempStack.push(current);
        // }
        // while (tempStack.size > 0){
        //     this.push(tempStack.pop());
        // }
        // return max;
        int max = (int) a[0];  
        for (int i = 1; i < size; i++){
            if ((int) a[i] > max){
                max = (int) a[i];
            }
        } 
        return max;
    }

    public int getmin(){
        if (size == 0) throw new IllegalStateException("Stack is empty");
        int min = (int) a[0];
        for (int i = 1; i < size ; i++){
            if ((int) a[i] < min){
                min = (int) a[i];

            }
        }
        return min;
    }
    
    @Override
    public String toString(){
        StringBuffer sb = new StringBuffer();
        sb.append ("[ ");
        for (int i = 0; i < size; i++){
            sb.append(a[i]);
            if (i < size - 1){
                sb.append(", ");
            }
        }
        sb.append(" ]");
        return sb.toString();
    }

    // public LinkedStack toLinkedStack(){
    //     LinkedStack temp = new LinkedStack();
    //     for (int i = 0; i < this.size; i++){
    //         temp.push(a[i]);
    //     }
    //     return temp;
    // }

    public boolean equals(ArrayStack arr){
        if (this.size != arr.size)
            return false;
        
        for (int i = 0; i < this.size; i++){
            if (!this.a[i].equals(arr.a[i])){
                return false;
            }
        }
        return true;
    }

    public ArrayStack[] split(){
        ArrayStack[] arr = new ArrayStack[2];
        int mid = size / 2;
        int s = size;

        arr[0] = new ArrayStack(mid);
        arr[1] = new ArrayStack(s - mid);

        for (int i = 0; i < mid; i++){
            arr[0].push(a[i]);
        }
        for (int i = mid; i < s ; i++){
            arr[1].push(a[i]);
        }
        return arr;
    }

    // Ye neeche waale process m stack khali ho jaayega, isliye use nahi kiya.

    // public ArrayStack[] split(ArrayStack arr){
    //     int s = arr.size();
    //     int mid = s / 2;
    //     ArrayStack a1 = new ArrayStack(size);
    //     ArrayStack a2 = new ArrayStack(size);

    //     for (int i = 0; i < mid; i++){
    //         a1.push(arr.pop());
    //     }
    //     for (int i = mid; i < s; i++){
    //         a2.push(arr.pop());
    //     }
    //     return new ArrayStack[]{a1, a2};

    // }

    public ArrayStack merge(ArrayStack arr){
        ArrayStack mergedStack = new ArrayStack(this.size + arr.size);
        for (int i = 0; i < this.size; i++){
            mergedStack.push(this.a[i]);
        }
        for (int i = 0; i < arr.size; i++){
            mergedStack.push(arr.a[i]);
        }
        return mergedStack;
    }

    public ArrayStack clone(ArrayStack arr){
        ArrayStack cloned = new ArrayStack(arr.size);
        for (int i = 0; i < arr.size; i++){
            cloned.push(arr.a[i]);
        }
        return cloned;
    }
}