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算法Sedgewick第四版-第1章基础-021一双向链表，在遍历时可修改、删除元素
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package algorithms.ADT; /******************************************************************************
* Compilation: javac DoublyLinkedList.java
* Execution: java DoublyLinkedList
* Dependencies: StdOut.java
*
* A list implemented with a doubly linked list. The elements are stored
* (and iterated over) in the same order that they are inserted.
*
* % java DoublyLinkedList 10
* 10 random integers between 0 and 99
* 24 65 2 39 86 24 50 47 13 4
*
* add 1 to each element via next() and set()
* 25 66 3 40 87 25 51 48 14 5
*
* multiply each element by 3 via previous() and set()
* 75 198 9 120 261 75 153 144 42 15
*
* remove elements that are a multiple of 4 via next() and remove()
* 75 198 9 261 75 153 42 15
*
* remove elements that are even via previous() and remove()
* 75 9 261 75 153 15
*
******************************************************************************/ import java.util.ListIterator;
import java.util.NoSuchElementException; import algorithms.util.StdOut;
import algorithms.util.StdRandom; public class DoublyLinkedList<Item> implements Iterable<Item> {
private int N; // number of elements on list
private Node pre; // sentinel before first item
private Node post; // sentinel after last item public DoublyLinkedList() {
pre = new Node();
post = new Node();
pre.next = post;
post.prev = pre;
} // linked list node helper data type
private class Node {
private Item item;
private Node next;
private Node prev;
} public boolean isEmpty() { return N == 0; }
public int size() { return N; } // add the item to the list
public void add(Item item) {
Node last = post.prev;
Node x = new Node();
x.item = item;
x.next = post;
x.prev = last;
post.prev = x;
last.next = x;
N++;
} public ListIterator<Item> iterator() { return new DoublyLinkedListIterator(); } // assumes no calls to DoublyLinkedList.add() during iteration
private class DoublyLinkedListIterator implements ListIterator<Item> {
private Node current = pre.next; // the node that is returned by next()
private Node lastAccessed = null; // the last node to be returned by prev() or next()
// reset to null upon intervening remove() or add()
private int index = 0; public boolean hasNext() { return index < N; }
public boolean hasPrevious() { return index > 0; }
public int previousIndex() { return index - 1; }
public int nextIndex() { return index; } public Item next() {
if (!hasNext()) throw new NoSuchElementException();
lastAccessed = current;
Item item = current.item;
current = current.next;
index++;
return item;
} public Item previous() {
if (!hasPrevious()) throw new NoSuchElementException();
current = current.prev;
index--;
lastAccessed = current;
return current.item;
} // replace the item of the element that was last accessed by next() or previous()
// condition: no calls to remove() or add() after last call to next() or previous()
public void set(Item item) {
if (lastAccessed == null) throw new IllegalStateException();
lastAccessed.item = item;
} // remove the element that was last accessed by next() or previous()
// condition: no calls to remove() or add() after last call to next() or previous()
public void remove() {
if (lastAccessed == null) throw new IllegalStateException();
Node x = lastAccessed.prev;
Node y = lastAccessed.next;
x.next = y;
y.prev = x;
N--;
if (current == lastAccessed)
current = y;
else
index--;
lastAccessed = null;
} // add element to list
public void add(Item item) {
Node x = current.prev;
Node y = new Node();
Node z = current;
y.item = item;
x.next = y;
y.next = z;
z.prev = y;
y.prev = x;
N++;
index++;
lastAccessed = null;
} } public String toString() {
StringBuilder s = new StringBuilder();
for (Item item : this)
s.append(item + " ");
return s.toString();
} // a test client
public static void main(String[] args) {
int N = Integer.parseInt(args[0]); // add elements 1, ..., N
StdOut.println(N + " random integers between 0 and 99");
DoublyLinkedList<Integer> list = new DoublyLinkedList<Integer>();
for (int i = 0; i < N; i++)
list.add(StdRandom.uniform(100));
StdOut.println(list);
StdOut.println(); ListIterator<Integer> iterator = list.iterator(); // go forwards with next() and set()
StdOut.println("add 1 to each element via next() and set()");
while (iterator.hasNext()) {
int x = iterator.next();
iterator.set(x + 1);
}
StdOut.println(list);
StdOut.println(); // go backwards with previous() and set()
StdOut.println("multiply each element by 3 via previous() and set()");
while (iterator.hasPrevious()) {
int x = iterator.previous();
iterator.set(x + x + x);
}
StdOut.println(list);
StdOut.println(); // remove all elements that are multiples of 4 via next() and remove()
StdOut.println("remove elements that are a multiple of 4 via next() and remove()");
while (iterator.hasNext()) {
int x = iterator.next();
if (x % 4 == 0) iterator.remove();
}
StdOut.println(list);
StdOut.println(); // remove all even elements via previous() and remove()
StdOut.println("remove elements that are even via previous() and remove()");
while (iterator.hasPrevious()) {
int x = iterator.previous();
if (x % 2 == 0) iterator.remove();
}
StdOut.println(list);
StdOut.println(); // add elements via next() and add()
StdOut.println("add elements via next() and add()");
while (iterator.hasNext()) {
int x = iterator.next();
iterator.add(x + 1);
}
StdOut.println(list);
StdOut.println(); // add elements via previous() and add()
StdOut.println("add elements via previous() and add()");
while (iterator.hasPrevious()) {
int x = iterator.previous();
iterator.add(x * 10);
iterator.previous();
}
StdOut.println(list);
StdOut.println();
}
}
