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MinPQ.java
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174 lines (144 loc) · 3.45 KB
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package com.algs;
import java.util.Iterator;
import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;
public class MinPQ<Key extends Comparable<Key>>
{
private Key[] pq;
private int N;
public MinPQ()
{
this(1 << 4);
}
@SuppressWarnings("unchecked")
public MinPQ(int capacity)
{
pq = (Key[]) new Comparable[capacity];
N = 0;
}
public MinPQ(Key[] keys)
{
}
public boolean isEmpty()
{
return N == 0;
}
public int size()
{
return N;
}
public void insert(Key key)
{
if(N > 0 && N == pq.length) resize(2 * pq.length);
pq[++N] = key;
swin(N);
assert isMinPQ();
}
public Key min()
{
return pq[1];
}
public Key delMin()
{
Key min = pq[1];
exch(1, N--);
pq[N + 1] = null;
if(N > 0 && N == pq.length / 4) resize(pq.length / 2);
sink(1);
assert isMinPQ();
return min;
}
public void sink(int k)
{
while(2 * k < N)
{
int j = 2 * k;
if(j < N && less(j + 1, j)) j++;
if(less(k, j)) break;
exch(k, j);
k = j;
}
}
public void swin(int k)
{
while(k > 1 && less(k, k/2))
{
exch(k/2, k);
k = k/2;
}
}
public boolean isMinPQ()
{
return isMinPQ(1);
}
public boolean isMinPQ(int k)
{
if(k > N) return true;
int left = 2 * k, right = 2 * k + 1;
if(left > N && less(left, k)) return false;
if(left > N && less(right, k)) return false;
return isMinPQ(left) && isMinPQ(right);
}
private void resize(int capacity)
{
assert capacity > N;
@SuppressWarnings("unchecked")
Key[] temp = (Key[]) new Comparable[capacity + 1];
System.arraycopy(pq, 0, temp, 0, N);
pq = temp;
}
private boolean less(int i, int j)
{
return pq[i].compareTo(pq[j]) < 0;
}
private void exch(int i, int j)
{
Key t = pq[i];
pq[i] = pq[j];
pq[j] = t;
}
public Iterator<Key> iterator()
{
return new HeapIterator();
}
public class HeapIterator implements Iterator<Key>
{
private MinPQ<Key> clone;
public HeapIterator()
{
clone = new MinPQ<>(size());
for(int i = 1; i < size(); i++) clone.insert(pq[i]);
}
@Override
public boolean hasNext()
{
return !clone.isEmpty();
}
@Override
public Key next()
{
if(!hasNext()) throw new UnsupportedOperationException(); ;
return clone.delMin();
}
public void remove()
{
throw new UnsupportedOperationException();
}
}
/**
* A test client.
*/
public static void main(String[] args) {
MinPQ<String> pq = new MinPQ<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")){
pq.insert(item);
}
else if (!pq.isEmpty()){
StdOut.print(pq.delMin() + " ");
}
}
StdOut.println("(" + pq.size() + " left on pq)");
}
}