队列的实现

实现Queue类

Java版本

使用链表结构作为实现的基础

          Queue就是队列，也就是说元素可以从队列的末尾加入队列中，但若需要删除元素，就需要在队列的开头将元素删除，删除元素也叫作出列。

import java.util.Iterator;import java.util.NoSuchElementException;import java.util.Arrays;public class Queue<T> implements Iterable<T>{private int count;private Node<T> first;private Node<T> last;private static class Node<T>{private T elem;private Node<T> next;}public Queue() {  }@SuppressWarnings("unchecked")public Queue( Queue<T> other ){Object[] array = new Object[other.size()];int i = 0;for( T elem : other )array[i++] = elem;T[] arrayCopy = ( T[] )Arrays.copyOf( array, array.length, Object[].class );for( T elem : arrayCopy )enqueue( elem );}public void enqueue( T elem ){Node<T> temp = new Node<>();temp.elem = elem;if( isEmpty() )first = temp;elselast.next = temp;last = temp;count++;}public T dequeue(){if( isEmpty() )throw new NoSuchElementException( "Queue underflow" );T elem = first.elem;first = first.next;if( isEmpty() )last = null;count--;return elem;}public T peek(){if( isEmpty() )throw new NoSuchElementException( "Queue underflow" );return first.elem;}public String toString(){StringBuilder s = new StringBuilder();s.append( "[ " );for( T elem : this )s.append( elem + " " );s.append( "]" );return s.toString();}public boolean isEmpty(){return first == null;}public int size(){return count;}private class ListIterator implements Iterator<T>{private Node<T> current = first;@Overridepublic boolean hasNext(){return current != null;}@Override public T next(){if( !hasNext() )throw new NoSuchElementException();T elem = current.elem;current = current.next;return elem;}@Overridepublic void remove(){throw new UnsupportedOperationException();}}@Overridepublic Iterator<T> iterator(){return new ListIterator();}}

使用环形数组作为实现的基础

           在使用数组实现队列时，通常有一个问题，就是在队列的头部删除元素时，由于数组中的元素是没有办法移动的，这就造成了在删除元素之后，数组头部出现了未填充的状态，造成了不必要的存储空间的浪费。所谓的环形数组，其实就是使用一般的数组，只不过若元素加在数组的末尾，这时要是数组末尾没有空余的位置，那么就可以将新的元素填充到数组开头的没有被利用的部分，要是整个数组都填满了元素，那么数组就会动态地增长。

import java.util.Iterator;import java.util.NoSuchElementException;public class ResizingArrayQueue<T> implements Iterable<T>{private T[] data;private int count;private int first;private int last;@SuppressWarnings("unchecked")public ResizingArrayQueue(){data = ( T[] )new Object[2];}public boolean isEmpty(){return count == 0;}public int size(){return count;}@SuppressWarnings("unchecked")private void resize( int newSize ){assert newSize >= count;T[] temp = ( T[] )new Object[newSize];for( int i = 0; i < count; i++ )temp[i] = data[ ( i + first ) % data.length];data = temp;first = 0;last = count;}public void enqueue( T elem ){if( count == data.length )resize( count * 2 );data[last] = elem;last = ( last + 1 ) % data.length;count++;}public T dequeue(){if( isEmpty() )throw new NoSuchElementException( "Queue underflow" );T elem = data[first];data[first] = null;first = ( first + 1 ) % data.length;count--;if( count > 0 && count == data.length / 4 )resize( data.length / 2 );return elem;}public T peek(){if( isEmpty() )throw new NoSuchElementException( "Queue underflow" );return data[first];}public Iterator<T> iterator(){return new ArrayIterator();}private class ArrayIterator implements Iterator<T>{private int current = first;@Overridepublic boolean hasNext(){return current != last;}@Overridepublic T next(){if( !hasNext() )throw new NoSuchElementException();T elem = data[current];current = ( current + 1 ) % data.length;return elem;}@Overridepublic void remove(){throw new UnsupportedOperationException();}}}

C++版本

待续...