001
002
003
004
005
006
007
008
009
010
011
012
013
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
029
030
031
032
033
034
035
036
037
038
039
040
041
042
043
044
045
046
047
048
049
050
051
052
053
054
055
056
057
058
059
060
061
062
063
064
065
066
067
068
069
070
071
072
073
074
075
076
077
078
079
080
081
082
083
084
085
086
087
088
089
090
091
092
093
094
095
096
097
098
099
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
// Exercise 1.3.14 (Solution published at http://algs4.cs.princeton.edu/)
package algs13;
import stdlib.*;
import java.util.Iterator;
import java.util.NoSuchElementException;
/* ***********************************************************************
 *  Compilation:  javac ResizingArrayQueue.java
 *  Execution:    java ResizingArrayQueue < input.txt
 *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
 *
 *  Queue implementation with a resizing array.
 *
 *  % java ResizingArrayQueue < tobe.txt
 *  to be or not to be (2 left on queue)
 *
 *************************************************************************/

public class ResizingArrayQueue<T> implements Iterable<T> {
  private T[] q;           // queue elements
  private int N;           // number of elements on queue
  private int first;       // index of first element of queue
  private int last;        // index of next available slot

  // cast needed since no generic array creation in Java
  @SuppressWarnings("unchecked")
  public ResizingArrayQueue() {
    this.q = (T[]) new Object[2];
    this.N = 0;
    this.first = 0;
    this.last = 0;
  }

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

  @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] = q[(first + i) % q.length];
    q = temp;
    first = 0;
    last  = N;
  }

  public void enqueue(T item) {
    if (N == q.length) resize(2*q.length);   // double size of array if necessary
    q[last] = item;                          // add item
    last = (last + 1) % q.length;
    N++;
  }

  // remove the least recently added item
  public T dequeue() {
    if (isEmpty()) throw new Error("Queue underflow");
    T item = q[first];
    q[first] = null;                         // to avoid loitering
    N--;
    first = (first + 1) % q.length;
    if (N > 0 && N == q.length/4) resize(q.length/2); // shrink size of array if necessary
    return item;
  }

  public Iterator<T> iterator() { return new ArrayIterator(); }
  private class ArrayIterator implements Iterator<T> {
    private int i = 0;
    public boolean hasNext()  { return i < N;                               }
    public void remove()      { throw new UnsupportedOperationException();  }

    public T next() {
      if (!hasNext()) throw new NoSuchElementException();
      T item = q[(first + i) % q.length];
      i++;
      return item;
    }
  }

  public String toString () {
    if (isEmpty()) return "[]";
    StringBuilder sb = new StringBuilder ("[");
    Iterator<T> i = iterator();
    sb.append (i.next ());
    while (i.hasNext ()) {
      sb.append (" ");
      sb.append (i.next ());
    }
    sb.append ("]");
    return sb.toString ();
  }
  private void check (String expected) {
    if (N<0 || N>q.length) throw new Error ();
    if (N==0 && q.length!=2) throw new Error ("Expected length 2, got " + q.length);
    if (N!=0 && N<q.length/4) throw new Error ();
    if (((first + N) % q.length) != last) throw new Error ();
    for (int i=0; i<N; i++) {
      if (q[(first + i) % q.length] == null) throw new Error ();
    }
    for (int i=N; i<q.length; i++) {
      if (q[(first + i) % q.length] != null) throw new Error ();
    }
    if (expected != null) {
      if (!expected.equals(this.toString ())) throw new Error ("Expected \"" + expected + "\", got \"" + this + "\"");
    }
    StdOut.println (this);
  }
  private void check (T iExpected, T iActual, String expected) {
    if (!iExpected.equals (iActual)) throw new Error ("Expected \"" + iExpected + "\", got \"" + iActual + "\"");
    check (expected);
  }
  public static void mainx (String args[]) {
    ResizingArrayQueue<Integer> d1;
    Integer k;
    d1 = new ResizingArrayQueue<> ();
    d1.enqueue (11); d1.check ("[11]");
    d1.enqueue (12); d1.check ("[11 12]");
    k = d1.dequeue(); d1.check (11, k, "[12]");
    k = d1.dequeue(); d1.check (12, k, "[]");

    d1 = new ResizingArrayQueue<> ();
    for (int i = 10; i < 20; i++)
      d1.enqueue (i);
    d1.check ("[10 11 12 13 14 15 16 17 18 19]");

    for (int i = 0; i < 10; i++) {
      d1.dequeue (); d1.check (null);
    }
    try { d1.dequeue (); throw new Error ("Expected exception"); } catch (Error e) {}
  }

  // A test client
  public static void main (String[] args) {
    StdIn.fromString ("to be or not to - be - - that - - - is");

    ResizingArrayQueue<String> q = new ResizingArrayQueue<>();
    while (!StdIn.isEmpty()) {
      String item = StdIn.readString();
      if (!item.equals("-")) q.enqueue(item);
      else StdOut.print(q.dequeue() + " ");
    }
    StdOut.println("(" + q.size() + " left on queue)");
  }
}