我正在用java中的跳過列表實現。基本上一切正常,但put
方法需要太長的時間來執行。這裏是我的代碼,我已經通過教程並查看了一些人的代碼,我似乎沒有看到問題出在哪裏(如果您測量放置100000個隨機元素需要幾年才能運行)。Java跳過列表實現優化
public class SkipList<K,V> {
private final SkipListItem<K,V> head;
private int currentLevel = 0;
private static final Random random = new Random();
private int height = 0;
public SkipList() {
this.head = new SkipListItem<>(null, null);
}
public V put(K key, V value) {
return this.put(key, value, null, 0);
}
private V put(K key, V value, SkipListItem<K,V> previous, int level) {
if(level > this.height) {
for(int i=0,s=level-this.height ; i<s ; ++i) {
this.addHeadItem();
}
}
SkipListItem<K,V> addedItem = new SkipListItem<>(key, value);
SkipListItem<K,V> insertAfter = this.findLowerItem(key, level);
addedItem.setPrevious(insertAfter);
if(insertAfter.getNext() != null) {
insertAfter.getNext().setPrevious(addedItem);
addedItem.setNext(insertAfter.getNext());
}
insertAfter.setNext(addedItem);
if(previous != null) {
addedItem.setBelow(previous);
previous.setAbove(addedItem);
}
return (SkipList.random.nextBoolean()) ? this.put(key, value, addedItem, level+1) : value ;
}
private void addHeadItem() {
SkipListItem<K,V> item = this.head;
while(item.getAbove() != null) {
item = item.getAbove();
}
SkipListItem<K,V> newHead = new SkipListItem<>(null,null);
item.setAbove(newHead);
newHead.setBelow(item);
++this.height;
}
private SkipListItem<K,V> findLowerItem(K key) {
return this.findLowerItem(key,0);
}
private SkipListItem<K,V> findLowerItem(K key, int level) {
SkipListItem<K,V> currentItem = this.head;
for(int i=0 ; i<level ; ++i) {
currentItem = currentItem.getAbove();
}
while( currentItem.getNext() != null &&
currentItem.getNext().getKey() != null &&
currentItem.getNext().compareTo(key) < 0) {
currentItem = currentItem.getNext();
}
return currentItem;
}
//...some other functions...
}
有什麼想法爲什麼需要這麼長時間?
做一些方法分析。什麼需要這麼久? (http://stackoverflow.com/questions/2267594/java-profiling-how-can-i-get-a-method-by-method-analysis-of-my-application或一些手冊'System.nanoTime()'聚合) – zapl
您可以包含「SkipListItem」的代碼嗎? –
您是否嘗試了一步一步的調試以確保'put()'的行爲符合預期(即使用索引而不是0級列表進行搜索並正確構建索引)? –