我正在尝试编写一个程序，该程序读取书籍的顺序，将它们存储在堆中并实现一种贪婪的算法，以便根据权重将书籍打包成盒子;
我无法正确实现堆。
我用来添加到Heap的方法称为addLastChild（）。它应该找到堆中的下一个位置并插入新书并根据其重量进行重组。
这是添加代码：
public void addLastChild(Book newBook)
{
Book[] pathList = new Book[30];
int tracker = 0;
int cnt = BookCnt+1;
String path = "";
while(cnt >= 1)
{
path = (cnt %2) + path;
cnt = cnt / 2;
}
Book c = root;
if(root!=null)
{
pathList[tracker]=root;
tracker++;
}
for(int i = 1; i < path.length()-1; i++){
if(path.charAt(i)== '0') {
c = c.left;
pathList[tracker]=c;
tracker++;
} else {
c = c.right;
pathList[tracker]=c;
tracker++;
}
}
if(path.length() == 1)
{
root = newBook;
}
else if(path.charAt(path.length()-1)== '0') {
c.left = newBook;
pathList[tracker]=c.left;
tracker++;
}
else
{
c.right = newBook;
pathList[tracker]=c.right;
tracker++;
}
BookCnt++;
boolean doTrickle = false;
if(tracker>=2)
{
doTrickle = true;
}
while(doTrickle == true)
{
Book temp = new Book(pathList[tracker-2].refNumber, pathList[tracker-2].weight, pathList[tracker-2].title, null,null);
//int refNumber, int weight, String title, Book left, Book right
print(root," ");
if(pathList[tracker-1].weight > pathList[tracker-2].weight)
{
pathList[tracker-2].refNumber=pathList[tracker-1].refNumber;
pathList[tracker-2].title=pathList[tracker-1].title;
pathList[tracker-2].weight=pathList[tracker-1].weight;
if(pathList[tracker-2].left == pathList[tracker-1])
{
pathList[tracker-2].left = temp;
}
if(pathList[tracker-2].right == pathList[tracker-1])
{
pathList[tracker-2].right = temp;
}
tracker--;
System.out.println("we trickled");
print(root," ");
}
else
{
doTrickle =false;
}
}
}
我用来从Heap中删除的两个方法是removeLastChild（）和remove（）removeLastChild（）方法返回堆中的最后一本书，而remove（）应该返回权重最大的书和用最后一本Book替换root，然后相应地重构堆。
以下是给我带来麻烦的删除代码：
Book removeLastChild() {
int cnt = BookCnt;
String path = "";
while(cnt >= 1)
{
path = (cnt %2) + path;
cnt = cnt / 2;
}
Book returnBook = null;
Book c = root;
for(int i = 1; i < path.length()-1; i++){
if(path.charAt(i)== '0') {
c = c.left;
} else {
c = c.right;
}
}
if(path.length() == 1)
{
returnBook = root;
root = null;
}
else if(path.charAt(path.length()-1)== '0') {
returnBook = c.left;
c.left = null;
}
else
{
returnBook = c.right;
c.right = null;
}
BookCnt--;
return returnBook;
}
Book remove()
{
Book largest =root;
root = removeLastChild();
if(largest.left!= null)
{
root.left = largest.left;
}
if(largest.right!= null)
{
root.right = largest.right;
}
Book cur = root;
if(root!= null)
{
while(cur.left !=null && cur.right!= null)
{
if(cur.weight<cur.left.weight || cur.weight<cur.right.weight)
{
Book temp = new Book(cur.refNumber, cur.weight, cur.title, null, null);
//int refNumber, int weight, String title, Book left, Book right
if(cur.left.weight>cur.right.weight)
{
cur.refNumber = cur.left.refNumber;
cur.title = cur.left.title;
cur.weight = cur.left.weight;
cur.left.refNumber = temp.refNumber;
cur.left.weight = temp.weight;
cur.left.title = temp.title;
cur = cur.left;
}
else
{
cur.refNumber = cur.right.refNumber;
cur.title = cur.right.title;
cur.weight = cur.right.weight;
cur.right.refNumber = temp.refNumber;
cur.right.weight = temp.weight;
cur.right.title = temp.title;
cur = cur.right;
}
}
else
{
return largest;
}
}
}
return largest;
}
感谢您的帮助！
我很乐意澄清任何我没有清楚沟通的内容。
答案 0 :(得分：1)
如果我可以建议您的堆实现的替代方案，并且考虑到针对背包问题的贪婪算法的目标，为什么不能简单地使用PriorityQueue？
来自文档：“基于优先级堆的无界优先级队列。优先级队列的元素根据其自然顺序排序，或者由队列构建时提供的比较器排序（...）”
如果您的图书类实现了这样的Comparable接口（示例中的Book非常简化）：
class Book implements Comparable<Book>{
public String title;
public int weight;
public Book(int weight, String title) {
this.weight = weight;
this.title = title;
}
@Override
public int compareTo(Book anotherBook) {
return weight - anotherBook.weight;
}
}
你的书的自然顺序应该从权重最小的书到最重的书。
在优先级队列中使用Book类：
public static void main(String[] args) {
Book book1 = new Book(10,"a");
Book book2 = new Book(11,"b");
Book book3 = new Book(20,"c");
Book book4 = new Book(20,"d");
Book book5 = new Book(11,"e");
PriorityQueue<Book> bookQueue = new PriorityQueue<Book>();
bookQueue.add(book1);
bookQueue.add(book2);
bookQueue.add(book3);
bookQueue.add(book4);
bookQueue.add(book5);
while(!bookQueue.isEmpty()){
Book book = bookQueue.poll();
System.out.println(book.title + " - " + book.weight);
}
}
您应该能够按照需要的方式对书籍进行迭代。