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package algs24;
import  stdlib.*;

/* ***********************************************************************
 *  Compilation:  javac IndexMinPQ.java
 *  Execution:    java IndexMinPQ
 *
 *  Minimum-oriented indexed PQ implementation using a binary heap.
 *
 *********************************************************************/

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 *  The <tt>IndexMinPQ</tt> class represents an indexed priority queue of generic keys.
 *  It supports the usual <em>insert</em> and <em>delete-the-minimum</em>
 *  operations, along with <em>delete</em> and <em>change-the-key</em>
 *  methods. In order to let the client refer to items on the priority queue,
 *  an integer between 0 and NMAX-1 is associated with each key&mdash;the client
 *  uses this integer to specify which key to delete or change.
 *  It also supports methods for peeking at the minimum key,
 *  testing if the priority queue is empty, and iterating through
 *  the keys.
 *  <p>
 *  The <em>insert</em>, <em>delete-the-minimum</em>, <em>delete</em>,
 *  <em>change-key</em>, <em>decrease-key</em>, and <em>increase-key</em>
 *  operations take logarithmic time.
 *  The <em>is-empty</em>, <em>size</em>, <em>min-index</em>, <em>min-key</em>, and <em>key-of</em>
 *  operations take constant time.
 *  Construction takes time proportional to the specified capacity.
 *  <p>
 *  This implementation uses a binary heap along with an array to associate
 *  keys with integers in the given range.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/24pq">Section 2.4</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */
public class IndexMinPQ<K extends Comparable<? super K>> implements Iterable<Integer> {
  private int NMAX;        // maximum number of elements on PQ
  private int N;           // number of elements on PQ
  private int[] pq;        // binary heap using 1-based indexing
  private int[] qp;        // inverse of pq - qp[pq[i]] = pq[qp[i]] = i
  private K[] keys;      // keys[i] = priority of i

  /**
   * Create an empty indexed priority queue with indices between 0 and NMAX-1.
   * @throws java.lang.IllegalArgumentException if NMAX < 0
   */
  @SuppressWarnings("unchecked")
  public IndexMinPQ(int NMAX) {
    if (NMAX < 0) throw new IllegalArgumentException();
    this.NMAX = NMAX;
    keys = (K[]) new Comparable[NMAX + 1];    // make this of length NMAX??
    pq   = new int[NMAX + 1];
    qp   = new int[NMAX + 1];                   // make this of length NMAX??
    for (int i = 0; i <= NMAX; i++) qp[i] = -1;
  }

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

  /**
   * Is i an index on the priority queue?
   * @throws java.lang.IndexOutOfBoundsException unless (0 &le; i < NMAX)
   */
  public boolean contains(int i) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    return qp[i] != -1;
  }

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

  /**
   * Associate key with index i.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.util.IllegalArgumentException if there already is an item associated with index i.
   */
  public void insert(int i, K key) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (contains(i)) throw new IllegalArgumentException("index is already in the priority queue");
    N++;
    qp[i] = N;
    pq[N] = i;
    keys[i] = key;
    swim(N);
  }

  /**
   * Return the index associated with a minimal key.
   * @throws java.util.NoSuchElementException if priority queue is empty.
   */
  public int minIndex() {
    if (N == 0) throw new NoSuchElementException("Priority queue underflow");
    return pq[1];
  }

  /**
   * Return a minimal key.
   * @throws java.util.NoSuchElementException if priority queue is empty.
   */
  public K minKey() {
    if (N == 0) throw new NoSuchElementException("Priority queue underflow");
    return keys[pq[1]];
  }

  /**
   * Delete a minimal key and return its associated index.
   * @throws java.util.NoSuchElementException if priority queue is empty.
   */
  public int delMin() {
    if (N == 0) throw new NoSuchElementException("Priority queue underflow");
    int min = pq[1];
    exch(1, N--);
    sink(1);
    qp[min] = -1;            // delete
    keys[pq[N+1]] = null;    // to help with garbage collection
    pq[N+1] = -1;            // not needed
    return min;
  }

  /**
   * Return the key associated with index i.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.util.NoSuchElementException no key is associated with index i
   */
  public K keyOf(int i) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
    else return keys[i];
  }

  /**
   * Change the key associated with index i to the specified value.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @deprecated Replaced by changeKey()
   */
  @Deprecated public void change(int i, K key) {
    changeKey(i, key);
  }

  /**
   * Change the key associated with index i to the specified value.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.util.NoSuchElementException no key is associated with index i
   */
  public void changeKey(int i, K key) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
    keys[i] = key;
    swim(qp[i]);
    sink(qp[i]);
  }

  /**
   * Decrease the key associated with index i to the specified value.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.lang.IllegalArgumentException if key &ge; key associated with index i
   * @throws java.util.NoSuchElementException no key is associated with index i
   */
  public void decreaseKey(int i, K key) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
    if (keys[i].compareTo(key) <= 0) throw new IllegalArgumentException("Calling decreaseKey() with given argument would not strictly decrease the key");
    keys[i] = key;
    swim(qp[i]);
  }

  /**
   * Increase the key associated with index i to the specified value.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.lang.IllegalArgumentException if key &le; key associated with index i
   * @throws java.util.NoSuchElementException no key is associated with index i
   */
  public void increaseKey(int i, K key) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
    if (keys[i].compareTo(key) >= 0) throw new IllegalArgumentException("Calling increaseKey() with given argument would not strictly increase the key");
    keys[i] = key;
    sink(qp[i]);
  }

  /**
   * Delete the key associated with index i.
   * @throws java.lang.IndexOutOfBoundsException unless 0 &le; i < NMAX
   * @throws java.util.NoSuchElementException no key is associated with index i
   */
  public void delete(int i) {
    if (i < 0 || i >= NMAX) throw new IndexOutOfBoundsException();
    if (!contains(i)) throw new NoSuchElementException("index is not in the priority queue");
    int index = qp[i];
    exch(index, N--);
    swim(index);
    sink(index);
    keys[i] = null;
    qp[i] = -1;
  }


  /* ************************************************************
   * General helper functions
   **************************************************************/
  private boolean greater(int i, int j) {
    return keys[pq[i]].compareTo(keys[pq[j]]) > 0;
  }

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


  /* ************************************************************
   * Heap helper functions
   **************************************************************/
  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;
    }
  }


  /* *********************************************************************
   * Iterators
   **********************************************************************/

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

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

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

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

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


  public static void main(String[] args) {
    // insert a bunch of strings
    String[] strings = { "it", "was", "the", "best", "of", "times", "it", "was", "the", "worst" };

    IndexMinPQ<String> pq = new IndexMinPQ<>(strings.length);
    for (int i = 0; i < strings.length; i++) {
      pq.insert(i, strings[i]);
    }

    // delete and print each key
    while (!pq.isEmpty()) {
      int i = pq.delMin();
      StdOut.println(i + " " + strings[i]);
    }
    StdOut.println();

    // reinsert the same strings
    for (int i = 0; i < strings.length; i++) {
      pq.insert(i, strings[i]);
    }

    // print each key using the iterator
    for (int i : pq) {
      StdOut.println(i + " " + strings[i]);
    }
    while (!pq.isEmpty()) {
      pq.delMin();
    }

  }
}