import java.util.Arrays;

public class Stack {

    // length of the array
    private static  int SIZE = 10;

    // the stack is an array
    private static int[] A = new int[SIZE];

    // cursor to next available slot in array, initialized to empty stack
    private static int next = 0;

    // put a new int on top of the stack
    public static void push(int n) {
        if (next == SIZE) {   // overflow!
            resize();
        }
        A[next] = n;
        ++next;
    }
    // Copied from HW 02
    private static void resize() {
        int[] T = new int[SIZE * 2];
        for(int i = 0; i < A.length; ++i) {
            T[i] = A[i];
        }
        SIZE = SIZE * 2;
        A = T;
    }

    // remove top int from the stack and return it
    public static int pop() {
        --next;
        int n = A[next];
        A[next] = 0;                  // not necessary, but shows structure of stack
        return n;
    }

    // return top int without removing it
    public static int top() {
        return A[next-1];
    }

    // number of ints in the stack
    public static int size() {
        return next;
    }

    // is the stack empty?
    public static boolean isEmpty() {
        return next == 0;

    }


    // just for debugging and tracing
    private static void printStack() {
        System.out.println("\nStack: " + Arrays.toString(A) + "\t next: " + next);
    }

    public static void main(String[] args) {

        System.out.println("\nUnit Test for Stack ADT");

        // test size and isEmpty on empty stack

        System.out.println("\nsize() => " + size());

        System.out.println("\nisEmpty() => " + isEmpty());

        System.out.println("\nPush 3, 6 and 7: ");
        push(3);
        push(6);
        push(7);

        printStack();

        System.out.println("\nsize() => " + size());

        System.out.println("\nisEmpty() => " + isEmpty());

        System.out.println("\npop() => " + pop());
        System.out.println("\npop() => " + pop());

        System.out.println("\nPush 7:");
        push(7);
        printStack();

        System.out.println("\nsize() => " + size());

        System.out.println("\nisEmpty() => " + isEmpty());

        //  Now test resizing

        for(int i = 9; i<100; i += 2) {
            push(i);
        }

        printStack();

        while(!isEmpty()) {
            pop();
        }

        printStack();

        System.out.println("\nsize() => " + size());

        System.out.println("\nisEmpty() => " + isEmpty());

    }
}