1：数据抽象
概念：
抽象数据类型，是一种能够对使用者隐藏数据表示的数据类型，抽象数据类型之所以重要，是因为他在程序设计上支持封装。
本节目标：本节将介绍三种抽象类型，用java实现，背包，堆栈，队列等最简单的数据结构。
- 背包 背包是一种不支持从中删除元素的集合数据类型。他的目的就是帮助用例手机元素并迭代遍历所有收集到的元素。API图示参考1.1
import java.util.Iterator; import java.util.NoSuchElementException; /** bag数据结构的实现 后进先出 不支持删除元素 */ public class Bag<Item> implements Iterable<Item> { private int N; private Node<Item> first; // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Is this bag empty? * * @return true if this bag is empty; false otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this bag. * * @return the number of items in this bag */ public int size() { return N; } /** * Adds the item to this bag. * * @param item the item to add to this bag */ public void add(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; N++; } /** * Initializes an empty bag. */ public Bag() { N = 0; first = null; } @Override public Iterator<Item> iterator() { return new ListIterator<Item>(first); } private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } @Override public boolean hasNext() { return current != null; } @Override public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } @Override public void remove() { throw new UnsupportedOperationException(); } } } - 队列 先进先出 可以联想在剧院门前排队等待入门的人
先进先出的队列结构，FIFO。Code实现
-
package com.luochuang.demo.stdlib; import org.w3c.dom.ls.LSException; import java.util.Iterator; import java.util.NoSuchElementException; public class Queue<Item> implements Iterable<Item> { private int N;// number of element on queue private Node<Item> first;// beginning of queue private Node<Item> last;// end of queue public class Node<Item> { private Node<Item> next; private Item item; } public Item peek() { if (isEmpty()) { throw new NoSuchElementException(); } return first.item; } /** * add item to queue * * @param item the item to add */ public void enQueue(Item item) { Node<Item> oldlast = last; last = new Node<Item>(); last.item = item; last.next = null; if (isEmpty()) { first = last; } else { oldlast.next = last; } N++; } /** * Removes and returns the item on this queue that was least recently added. * * @return the item on this queue that was least recently added * @throws java.util.NoSuchElementException if this queue is empty */ public Item deQueue() { if (isEmpty()) { throw new NoSuchElementException(); } Item item = first.item; first = first.next; N--; if (isEmpty()) { last = null; } return item; } /** * is this queue empty? * * @return true if this queue is empty otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this queue. * * @return the number of items in this queue */ public int size() { return N; } /** * Initializes an empty queue. */ public Queue() { first = null; last = null; N = 0; } @Override public Iterator<Item> iterator() { return null; } public class ListIterator implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { first = current; } @Override public boolean hasNext() { return current == null; } @Override public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } @Override public void remove() { throw new UnsupportedOperationException(); } } }
- 下压栈
下压栈是一种基于后进先出的队列结构，LIFO。比如点击超级链接中的按钮，当回退之后能重新访问之前的页面，即从栈中弹出。也可以联想桌面上放的一匝便签.
package com.luochuang.demo.stdlib;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class Stack<Item> implements Iterable<Item> {
private int N;
private Node<Item> first;
/**
* Initializes an empty stack
*/
public Stack() {
first = null;
N = 0;
}
/**
* Adds the item to this stack.
* @param item the item to add
*/
public void push(Item item) {
Node<Item> oldfirst = first;
first = new Node<Item>();
first.item = item;
first.next = oldfirst;
N++;
}
/**
* Removes and returns the item most recently added to this stack.
*
* @return the item most recently added
* @throws java.util.NoSuchElementException if this stack is empty
*/
public Item pop() {
if (isEmpty())
throw new NoSuchElementException("Stack underflow");
Item item = first.item; // save item to return
first = first.next; // delete first node
N--;
return item; // return the saved item
}
/**
* Returns (but does not remove) the item most recently added to this stack.
* @return the item most recently added to this stack
* @throws java.util.NoSuchElementException if this stack is empty
*/
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Stack underflow");
return first.item;
}
public boolean isEmpty() {
return first == null;
}
public int size() {
return N;
}
private class Node<Item> {
private Node<Item> next;
private Item item;
}
/**
* Returns a string representation of this stack.
* @return the sequence of items in the stack in LIFO order, separated by spaces
*/
public String toString() {
StringBuilder s = new StringBuilder();
for (Item item : this)
s.append(item + " ");
return s.toString();
}
@Override
public Iterator<Item> iterator() {
return new ListIterator(first);
}
public class ListIterator implements Iterator<Item> {
public Node<Item> current;
public ListIterator(Node<Item> first) {
first = current;
}
@Override
public boolean hasNext() {
return current == null;
}
@Override
public Item next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
Item item = current.item;
current = current.next;
return item;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
}
数据结构之背包,队列,栈
时间： 2024-10-05 21:22:03