001package algs24;
002import stdlib.*;
003import java.util.Iterator;
004import java.util.NoSuchElementException;
005/* ***********************************************************************
006 *  Compilation:  javac MaxPQ.java
007 *  Execution:    java MaxPQ < input.txt
008 *
009 *  Generic max priority queue implementation with a binary heap.
010 *
011 *  % java MaxPQ < tinyPQ.txt
012 *  Q X P (6 left on pq)
013 *
014 *  We use a one-based array to simplify parent and child calculations.
015 *
016 *************************************************************************/
017/* Modified by jriely@cs.depaul.edu */
018public class XFixedMaxPQ<K extends Comparable<? super K>> implements Iterable<K> {
019        private final K[] pq;                    // store items at indices 1 to N
020        private int N;                       // number of items on priority queue
021        private final int MAXN;
022
023        @SuppressWarnings("unchecked")
024        /** Create an empty priority queue with the given initial capacity, using the given comparator. */
025        public XFixedMaxPQ(int initCapacity) {
026                MAXN = initCapacity;
027                pq = (K[]) new Comparable[initCapacity + 1];
028                N = 0;
029        }
030
031        /** Is the priority queue empty? */
032        public boolean isEmpty() { return N == 0; }
033
034        /** Is the priority queue full? */
035        public boolean isFull()  { return N == MAXN; }
036
037        /** Return the number of items on the priority queue. */
038        public int size() { return N; }
039
040        /**
041         * Return the largest key on the priority queue.
042         * Throw an exception if the priority queue is empty.
043         */
044        public K max() {
045                if (isEmpty()) throw new Error("Priority queue underflow");
046                return pq[1];
047        }
048
049        /** Add a new key to the priority queue. */
050        public void insert(K x) {
051                if (isFull()) throw new Error("Priority queue overflow");
052
053                // add x, and percolate it up to maintain heap invariant
054                pq[++N] = x;
055                swim(N);
056                //assert isMaxHeap();
057        }
058
059        /**
060         * Delete and return the largest key on the priority queue.
061         * Throw an exception if the priority queue is empty.
062         */
063        public K delMax() {
064                if (N == 0) throw new Error("Priority queue underflow");
065                K max = pq[1];
066                exch(1, N--);
067                sink(1);
068                pq[N+1] = null; // avoid loitering and help with garbage collection
069                //assert isMaxHeap();
070                return max;
071        }
072
073
074        /* *********************************************************************
075         * Helper functions to restore the heap invariant.
076         **********************************************************************/
077
078        private void swim(int k) {
079                while (k > 1 && less(k/2, k)) {
080                        exch(k, k/2);
081                        k = k/2;
082                }
083        }
084
085        private void sink(int k) {
086                while (2*k <= N) {
087                        int j = 2*k;
088                        if (j < N && less(j, j+1)) j++;
089                        if (!less(k, j)) break;
090                        exch(k, j);
091                        k = j;
092                }
093        }
094
095        /* *********************************************************************
096         * Helper functions for compares and swaps.
097         **********************************************************************/
098        private boolean less(int i, int j) {
099                return pq[i].compareTo(pq[j]) < 0;
100        }
101
102        private void exch(int i, int j) {
103                K swap = pq[i];
104                pq[i] = pq[j];
105                pq[j] = swap;
106        }
107
108        // is pq[1..N] a max heap?
109        private boolean isMaxHeap() {
110                return isMaxHeap(1);
111        }
112
113        // is subtree of pq[1..N] rooted at k a max heap?
114        private boolean isMaxHeap(int k) {
115                if (k > N) return true;
116                int left = 2*k, right = 2*k + 1;
117                if (left  <= N && less(k, left))  return false;
118                if (right <= N && less(k, right)) return false;
119                return isMaxHeap(left) && isMaxHeap(right);
120        }
121
122
123        /* *********************************************************************
124         * Iterator
125         **********************************************************************/
126
127        /**
128         * Return an iterator that iterates over all of the keys on the priority queue
129         * in descending order.
130         * <p>
131         * The iterator doesn't implement {@code remove()} since it's optional.
132         */
133        public Iterator<K> iterator() { return new HeapIterator(); }
134
135        private class HeapIterator implements Iterator<K> {
136                // create a new pq
137                private final XFixedMaxPQ<K> copy;
138
139                // add all items to copy of heap
140                // takes linear time since already in heap order so no keys move
141                public HeapIterator() {
142                        copy = new XFixedMaxPQ<>(size());
143                        for (int i = 1; i <= N; i++)
144                                copy.insert(pq[i]);
145                }
146
147                public boolean hasNext()  { return !copy.isEmpty();                     }
148                public void remove()      { throw new UnsupportedOperationException();  }
149
150                public K next() {
151                        if (!hasNext()) throw new NoSuchElementException();
152                        return copy.delMax();
153                }
154        }
155
156        private void showHeap() {
157                for (int i = 1; i <= N; i++)
158                        StdOut.print (pq[i] + " ");
159                StdOut.println ();
160        }
161
162        /**
163         * A test client.
164         */
165        public static void main(String[] args) {
166                XFixedMaxPQ<String> pq = new XFixedMaxPQ<>(100);
167                StdIn.fromString("10 20 30 40 50 - - - 05 25 35 - - - 70 80 05 - - - - ");
168                while (!StdIn.isEmpty()) {
169                        StdOut.print ("pq:  "); pq.showHeap();
170                        String item = StdIn.readString();
171                        if (item.equals("-")) StdOut.println("max: " + pq.delMax());
172                        else pq.insert(item);
173                }
174                StdOut.println("(" + pq.size() + " left on pq)");
175        }
176
177}