package algs24;
import stdlib.*;
import java.util.Iterator;
import java.util.NoSuchElementException;
/* ***********************************************************************
 *  Compilation:  javac MinPQ.java
 *  Execution:    java MinPQ < input.txt
 *
 *  Generic min priority queue implementation with a binary heap.
 *
 *  % java MinPQ < tinyPQ.txt
 *  E A E (6 left on pq)
 *
 *  We use a one-based array to simplify parent and child calculations.
 *
 *************************************************************************/
/* Modified by jriely@cs.depaul.edu */
public class XFixedMinPQ<K extends Comparable<? super K>> implements Iterable<K> {
  private final K[] pq;                    // store items at indices 1 to N
  private int N;                       // number of items on priority queue
  private final int MAXN;

  /** Create an empty priority queue with the given initial capacity, using the given comparator. */
  @SuppressWarnings("unchecked")
  public XFixedMinPQ(int initCapacity) {
    MAXN = initCapacity;
    pq = (K[]) new Comparable[initCapacity + 1];
    N = 0;
  }

  /** Is the priority queue empty? */
  public boolean isEmpty() { return N == 0; }

  /** Is the priority queue full? */
  public boolean isFull()  { return N == MAXN; }

  /** Return the number of items on the priority queue. */
  public int size() { return N; }

  /**
   * Return the smallest key on the priority queue.
   * Throw an exception if the priority queue is empty.
   */
  public K min() {
    if (isEmpty()) throw new Error("Priority queue underflow");
    return pq[1];
  }

  /** Add a new key to the priority queue. */
  public void insert(K x) {
    if (isFull()) throw new Error("Priority queue overflow");

    // add x, and percolate it up to maintain heap invariant
    pq[++N] = x;
    swim(N);
    //assert isMinHeap();
  }

  /**
   * Delete and return the smallest key on the priority queue.
   * Throw an exception if the priority queue is empty.
   */
  public K delMin() {
    if (N == 0) throw new Error("Priority queue underflow");
    exch(1, N);
    K min = pq[N--];
    sink(1);
    pq[N+1] = null; // avoid loitering and help with garbage collection
    //assert isMinHeap();
    return min;
  }


  /* *********************************************************************
   * Helper functions to restore the heap invariant.
   **********************************************************************/

  private void swim(int k) {
    while (k > 1 && greater(k/2, k)) {
      exch(k, k/2);
      k = k/2;
    }
  }

  private void sink(int k) {
    while (2*k <= N) {
      int j = 2*k;
      if (j < N && greater(j, j+1)) j++;
      if (!greater(k, j)) break;
      exch(k, j);
      k = j;
    }
  }

  /* *********************************************************************
   * Helper functions for compares and swaps.
   **********************************************************************/
  private boolean greater(int i, int j) {
    return pq[i].compareTo(pq[j]) > 0;
  }

  private void exch(int i, int j) {
    K swap = pq[i];
    pq[i] = pq[j];
    pq[j] = swap;
  }

  // is pq[1..N] a min heap?
  private boolean isMinHeap() {
    return isMinHeap(1);
  }

  // is subtree of pq[1..N] rooted at k a min heap?
  private boolean isMinHeap(int k) {
    if (k > N) return true;
    int left = 2*k, right = 2*k + 1;
    if (left  <= N && greater(k, left))  return false;
    if (right <= N && greater(k, right)) return false;
    return isMinHeap(left) && isMinHeap(right);
  }


  /* *********************************************************************
   * Iterator
   **********************************************************************/

  /**
   * Return an iterator that iterates over all of the keys on the priority queue
   * in ascending order.
   * <p>
   * The iterator doesn't implement {@code remove()} since it's optional.
   */
  public Iterator<K> iterator() { return new HeapIterator(); }

  private class HeapIterator implements Iterator<K> {
    // create a new pq
    private final XFixedMinPQ<K> copy;

    // add all items to copy of heap
    // takes linear time since already in heap order so no keys move
    public HeapIterator() {
      copy = new XFixedMinPQ<>(size());
      for (int i = 1; i <= N; i++)
        copy.insert(pq[i]);
    }

    public boolean hasNext()  { return !copy.isEmpty();                     }
    public void remove()      { throw new UnsupportedOperationException();  }

    public K next() {
      if (!hasNext()) throw new NoSuchElementException();
      return copy.delMin();
    }
  }

  private void showHeap() {
    for (int i = 1; i <= N; i++)
      StdOut.print (pq[i] + " ");
    StdOut.println ();
  }

  /**
   * A test client.
   */
  public static void main(String[] args) {
    XFixedMinPQ<String> pq = new XFixedMinPQ<>(100);
    StdIn.fromString ("10 20 30 40 50 - - - 05 25 35 - - - 70 80 05 - - - - ");
    while (!StdIn.isEmpty()) {
      StdOut.print ("pq:  "); pq.showHeap();
      String item = StdIn.readString();
      if (item.equals("-")) StdOut.println("min: " + pq.delMin());
      else pq.insert(item);
    }
    StdOut.println("(" + pq.size() + " left on pq)");
  }
}