我在下面的replaceValue方法中得到了一个超出范围的索引，我不知道为什么。
[null，（10,4），（52,3），（39,9），（78,7），（63,8），（42,2），（50,411）]
重置价值测试：411 大小= 7
[null，（10,4），（52,3），（39,9），（78,7），（63,8），（42,2），（50,101）]
去除试验：（10,4）
[null，（39,9），（52,3），（42,2），（78,7），（63,8），（50,101）]
大小= 6
我尝试在此处再次替换该值并收到错误...
package heappriorityqueue;
import java.util.*;
public class HeapPriorityQueue<K,V> {
protected ArrayList<Entry<K,V>> heap;
protected Comparator<K> comp;
int size = 0;
protected static class MyEntry<K,V> implements Entry<K,V> {
protected K key;
protected V value;
protected int loc;
public MyEntry(K k, V v,int i) {key = k; value = v;loc =i;}
public K getKey() {return key;}
public V getValue() {return value;}
public int getLoc(){return loc;}
public String toString() {return "(" + key + "," + value + ")";}
void setKey(K k1) {key = k1;}
void setValue(V v1) {value = v1;}
public void setLoc(int i) {loc = i;}
}
public HeapPriorityQueue() {
heap = new ArrayList<Entry<K,V>>();
heap.add(0,null);
comp = new DefaultComparator<K>();
}
public HeapPriorityQueue(Comparator<K> c) {
heap = new ArrayList<Entry<K,V>>();
heap.add(0,null);
comp = c;
}
public int size() {return size;}
public boolean isEmpty() {return size == 0; }
public Entry<K,V> min() throws EmptyPriorityQueueException {
if (isEmpty())
throw new EmptyPriorityQueueException("Priority Queue is Empty");
return heap.get(1);
}
public Entry<K,V> insert(K k, V v) {
size++;
Entry<K,V> entry = new MyEntry<K,V>(k,v,size);
heap.add(size,entry);
upHeap(size);
return entry;
}
public Entry<K,V> removeMin() throws EmptyPriorityQueueException {
if (isEmpty())
throw new EmptyPriorityQueueException("Priority Queue is Empty");
if (size == 1)
return heap.remove(1);
Entry<K,V> min = heap.get(1);
heap.set(1, heap.remove(size));
size--;
downHeap(1);
return min;
}
public V replaceValue(Entry<K,V> e, V v) throws InvalidEntryException,
EmptyPriorityQueueException {
// replace the value field of entry e in the priority
// queue with the given value v, and return the old value
This is where I am getting the IndexOutOfBounds exception, on heap.get(i);
if (isEmpty()){
throw new EmptyPriorityQueueException("Priority Queue is Empty.");
}
checkEntry(e);
int i = e.getLoc();
Entry<K,V> entry=heap.get(((i)));
V oldVal = entry.getValue();
K key=entry.getKey();
Entry<K,V> insert = new MyEntry<K,V>(key,v,i);
heap.set(i, insert);
return oldVal;
}
public K replaceKey(Entry<K,V> e, K k) throws InvalidEntryException,
EmptyPriorityQueueException, InvalidKeyException {
// replace the key field of entry e in the priority
// queue with the given key k, and return the old key
if (isEmpty()){
throw new EmptyPriorityQueueException("Priority Queue is Empty.");
}
checkKey(k);
checkEntry(e);
K oldKey=e.getKey();
int i = e.getLoc();
Entry<K,V> entry = new MyEntry<K,V>(k,e.getValue(),i);
heap.set(i,entry);
downHeap(i);
upHeap(i);
return oldKey;
}
public Entry<K,V> remove(Entry<K,V> e) throws InvalidEntryException,
EmptyPriorityQueueException{
// remove entry e from priority queue and return it
if (isEmpty()){
throw new EmptyPriorityQueueException("Priority Queue is Empty.");
}
MyEntry<K,V> entry = checkEntry(e);
if (size==1){
return heap.remove(size--);
}
int i = e.getLoc();
heap.set(i, heap.remove(size--));
downHeap(i);
return entry;
}
protected void upHeap(int i) {
while (i > 1) {
if (comp.compare(heap.get(i/2).getKey(), heap.get(i).getKey()) <= 0)
break;
swap(i/2,i);
i = i/2;
}
}
protected void downHeap(int i) {
int smallerChild;
while (size >= 2*i) {
smallerChild = 2*i;
if ( size >= 2*i + 1)
if (comp.compare(heap.get(2*i + 1).getKey(), heap.get(2*i).getKey()) < 0)
smallerChild = 2*i+1;
if (comp.compare(heap.get(i).getKey(), heap.get(smallerChild).getKey()) <= 0)
break;
swap(i, smallerChild);
i = smallerChild;
}
}
protected void swap(int j, int i) {
heap.get(j).setLoc(i);
heap.get(i).setLoc(j);
Entry<K,V> temp;
temp = heap.get(j);
heap.set(j, heap.get(i));
heap.set(i, temp);
}
public String toString() {
return heap.toString();
}
protected MyEntry<K,V> checkEntry(Entry<K,V> ent)
throws InvalidEntryException
{
if(ent == null || !(ent instanceof MyEntry))
throw new InvalidEntryException("Invalid entry.");
return (MyEntry)ent;
}
protected void checkKey(K key) throws InvalidKeyException{
try{comp.compare(key,key);}
catch(Exception e){throw new InvalidKeyException("Invalid key.");}
}
}
HeapPriorityQueue<Integer,Integer> testPQ = new HeapPriorityQueue<Integer,Integer>();
System.out.print("[");
int x;
for (int i = 0; i < 10; i++) {
x = (int) (100 * Math.random());
System.out.print(" " + x);
testPQ.insert(x,i);
}
System.out.println("]");
System.out.println(testPQ);
for (int i = 0; i < 5; i++) {
System.out.println(testPQ.removeMin());
System.out.println(testPQ);
}
Entry e = testPQ.insert(10, 4);
System.out.println("insertion of "+e);
System.out.println(testPQ);
System.out.println("size="+testPQ.size);
System.out.println(e.getKey());
Entry r = testPQ.insert(50, 411);
System.out.println("insertion of "+r);
System.out.println("size="+testPQ.size);
System.out.println(testPQ);
System.out.println("replacement value test" +
testPQ.replaceValue(r, 101));
System.out.println("size="+testPQ.size);
System.out.println(testPQ);
System.out.println("removal test:"+testPQ.remove(e));
System.out.println(testPQ);
System.out.println("replacement value test" +
testPQ.replaceValue(r, 201));
System.out.println("replacement value test" +
testPQ.replaceValue(r, 301));
System.out.println("replacement value test" +
testPQ.replaceValue(r, 401));
System.out.println("size="+testPQ.size);
System.out.println(testPQ);
Entry k = testPQ.min();
System.out.println("replacement key test:"+testPQ.replaceKey(k,77)
+" w/77");
System.out.println(testPQ);
Entry v = testPQ.min();
System.out.println("replacement key test:"+testPQ.replaceKey(v,6)+
" w/6");
System.out.println(testPQ);
System.out.println("removal test:"+testPQ.remove(v));
System.out.println(testPQ);
run:
[ 17 86 13 52 98 4 9 25 6 75]
[null, (4,5), (6,8), (9,6), (25,7), (75,9), (17,0), (13,2), (86,1), (52,3), (98,4)]
(4,5)
[null, (6,8), (25,7), (9,6), (52,3), (75,9), (17,0), (13,2), (86,1), (98,4)]
(6,8)
[null, (9,6), (25,7), (13,2), (52,3), (75,9), (17,0), (98,4), (86,1)]
(9,6)
[null, (13,2), (25,7), (17,0), (52,3), (75,9), (86,1), (98,4)]
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 7, Size: 7
(13,2)
[null, (17,0), (25,7), (86,1), (52,3), (75,9), (98,4)]
(17,0)
[null, (25,7), (52,3), (86,1), (98,4), (75,9)]
insertion of (10,4)
[null, (10,4), (52,3), (25,7), (98,4), (75,9), (86,1)]
size=6
10
insertion of (50,411)
size=7
[null, (10,4), (52,3), (25,7), (98,4), (75,9), (86,1), (50,411)]
replacement value test411
size=7
[null, (10,4), (52,3), (25,7), (98,4), (75,9), (86,1), (50,101)]
removal test:(10,4)
[null, (25,7), (52,3), (50,101), (98,4), (75,9), (86,1)]
at java.util.ArrayList.rangeCheck(ArrayList.java:604)
at java.util.ArrayList.get(ArrayList.java:382)
at heappriorityqueue.HeapPriorityQueue.replaceValue(HeapPriorityQueue.java:283)
at heappriorityqueue.Main.main(Main.java:55)
Java结果：1 建立成功（总时间：0秒）
答案 0 :(得分：1)
您可以在条目本身中保存条目的数组索引。但是在您的remove()方法中，您不会更改它。您必须为更改位置的所有元素更改该索引，否则您将在进一步删除调用时删除错误的元素。
在您的示例中，(50,101)最初有索引6。删除后该值仍然存在，因此如果您尝试替换它，它仍会尝试访问不再存在的索引6（因为int i = e.getLoc();）。