CSC300: ResizingArrayStack [13/15] Previous pageContentsNext page

file:ResizingArrayStack.java [source] [doc-public] [doc-private]
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package algs13;
//import stdlib.*;
import java.util.Iterator;
import java.util.NoSuchElementException;
/* ***********************************************************************
 *  Compilation:  javac ResizingArrayStack.java
 *  Execution:    java ResizingArrayStack < input.txt
 *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
 *
 *  Stack implementation with a resizing array.
 *
 *  % more tobe.txt
 *  to be or not to - be - - that - - - is
 *
 *  % java ResizingArrayStack < tobe.txt
 *  to be not that or be (2 left on stack)
 *
 *************************************************************************/
public class ResizingArrayStack<T> implements Iterable<T> {
  private T[] a;        // array of items
  private int N;        // number of elements on stack

  // create an empty stack
  @SuppressWarnings("unchecked")
  public ResizingArrayStack() {
    this.a = (T[]) new Object[2];
    this.N = 0;
  }

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


  // resize the underlying array holding the elements
  @SuppressWarnings("unchecked")
  private void resize(int capacity) {
    if (capacity <= N) throw new IllegalArgumentException ();
    T[] temp = (T[]) new Object[capacity];
    for (int i = 0; i < N; i++)
      temp[i] = a[i];
    a = temp;
  }

  // push a new item onto the stack
  public void push(T item) {
    if (N == a.length) resize(2*N); // increase array size if necessary
    //if (N == a.length) resize(N + Math.max (1, N/1));
    a[N] = item;
    N++;
  }

  // delete and return the item most recently added
  public T pop() {
    if (isEmpty()) { throw new Error("Stack underflow error"); }
    N--;
    T item = a[N];
    a[N] = null; // to avoid loitering
    if (N > 0 && N == a.length/4) resize(a.length/2); // shrink size of array if necessary
    return item;
  }


  public Iterator<T> iterator()  { return new ReverseArrayIterator();  }

  // an iterator, doesn't implement remove() since it's optional
  private class ReverseArrayIterator implements Iterator<T> {
    private int i = N;
    public boolean hasNext()  { return i > 0;                               }
    public void remove()      { throw new UnsupportedOperationException();  }

    public T next() {
      if (!hasNext()) throw new NoSuchElementException();
      return a[--i];
    }
  }

  /* *********************************************************************
   * Test routine.
   **********************************************************************/
//  public static void bookMain(String[] args) {
//    StdIn.fromString ("to be or not to - be - - that - - - is");
//
//    ResizingArrayStack<String> s = new ResizingArrayStack<>();
//    while (!StdIn.isEmpty()) {
//      String item = StdIn.readString();
//      if (!item.equals("-")) s.push(item);
//      else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
//    }
//    StdOut.println("(" + s.size() + " left on stack)");
//  }
//
//  /* *********************************************************************
//   * Test routine.
//   **********************************************************************/
//  public static void main(String[] args) {
//    double prevTime = 1;
//    for (int i = 0, size = 16; i<20; i += 1, size *= 2) {
//      Stopwatch s = new Stopwatch ();
//
//      for (int k = 0; k < 100; k++) {
//        ResizingArrayStack<Double> stack = new ResizingArrayStack<> ();
//        for (int j = 0; j < size; j++) {
//          stack.push (1.2);
//        }
//      }
//
//      double thisTime = s.elapsedTime ();
//      StdOut.format ("size=%d thisTime=%f ratio=%f\n", size, thisTime, thisTime/prevTime);
//      prevTime = thisTime;
//    }
//  }
}

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