我正在尝试使用AVL树作为底层结构来实现一个简单的Map。我使用二叉搜索树作为底层结构实现了Map，但是我无法想象如何在必要时检查和平衡树。当我输入一个键值对时，我需要检查树的平衡并采取相应的行动。我不知道该怎么做。这是我的MyAVLMap代码（从二叉搜索树实现中利用）。任何帮助表示赞赏!!
这是我的班级：
public class MyAVLMap<K, V> implements BasicMap<K, V> {
// the root of the "tree" that structures the map
private AVLNode root;
// the number of key-value mappings currently in the map
private int numKeys;
/**
* Constructs MyAVLMap object.
*/
public MyAVLMap() {
root = null;
numKeys = 0;
}
/**
* Associates the specified value with the specified
* key in the current map.
*
* @param key The key with which the specified value
* is to be associated.
* @param value The value to be associated with the
* specified key.
*/
public void put(K key, V value){
// input validation
if(key == null || value == null) {
throw new IllegalArgumentException();
}
root = put(root, (Comparable) key, value);
}
// // This helper method adds the specified key-value mapping
// // to the tree rooted at "r".
// @SuppressWarnings("unchecked")
// private AVLNode put(AVLNode r, Comparable key, V value){
// if(r == null) {
// numKeys++;
// return new AVLNode(key, value);
// }
//
// int compare = key.compareTo(r.key);
// if(compare == 0) {
// r.value = value;
// } else if(compare < 0) {
// r.left = put(r.left, key, value);
// } else { // (compare > 0)
// r.right = put(r.right, key, value);
// }
//
// return r;
// }
/**
* Internal method to insert into a subtree.
*
* @param x the item to insert.
* @param t the node that roots the tree.
* @return the new root.
*/
@SuppressWarnings("unchecked")
private AVLNode put(AVLNode r, Comparable key, V value)
{
if(r == null) {
return new AVLNode(key, value);
} else if(key.compareTo(r.key) < 0) {
r.left = put(r.left, key, value);
if((r.left.height - r.right.height == 2) &&
(key.compareTo(r.left.key) < 0)) {
r = rotateWithLeftChild(r);
} else {
r = doubleWithLeftChild(r);
}
} else if(key.compareTo(r.key) > 0 ) {
r.right = put(r.right, key, value);
if((r.right.height - r.left.height == 2) &&
(key.compareTo(r.right.key) > 0)) {
r = rotateWithRightChild(r);
}
else {
r = doubleWithRightChild(r);
}
}
// else: Duplicate; do nothing
r.height = max(r.left.height, r.right.height) + 1;
return r;
}
// This helper method returns the greater of two integers.
private static int max(int n1, int n2)
{
if(n1 > n2) {
return n1;
} else { // left <= right
return n2;
}
}
/**
* Rotate binary tree node with left child.
* For AVL trees, this is a single rotation for case 1.
* Update heights, then return new root.
*/
private AVLNode rotateWithLeftChild(AVLNode root2) {
AVLNode root1 = root2.left;
root2.left = root1.right;
root1.right = root2;
root2.height = max(root2.left.height, root2.right.height) + 1;
root1.height = max(root1.left.height, root2.height) + 1;
return root1;
}
/**
* Rotate binary tree node with right child.
* For AVL trees, this is a single rotation for case 4.
* Update heights, then return new root.
*/
private AVLNode rotateWithRightChild(AVLNode root1) {
AVLNode root2 = root1.right;
root1.right = root2.left;
root2.left = root1;
root1.height = max(root1.left.height, root1.right.height) + 1;
root2.height = max(root2.right.height, root1.height) + 1;
return root2;
}
/**
* Double rotate binary tree node: first left child
* with its right child; then node k3 with new left child.
* For AVL trees, this is a double rotation for case 2.
* Update heights, then return new root.
*/
private AVLNode doubleWithLeftChild(AVLNode r) {
r.left = rotateWithRightChild(r.left);
return rotateWithLeftChild(r);
}
/**
* Double rotate binary tree node: first right child
* with its left child; then node r1 with new right child.
* For AVL trees, this is a double rotation for case 3.
* Update heights, then return new root.
*/
private AVLNode doubleWithRightChild(AVLNode r) {
r.right = rotateWithLeftChild(r.right);
return rotateWithRightChild(r);
}
/**
* Returns the value to which the specified key is mapped,
* or <tt>null</tt> if the specified key is not mapped.
*
* @param key The key whose associated value is to be returned.
* @return The value to which the specified key is mapped,
* or <tt>null</tt> if the specified key is not mapped.
*/
public V get(Object key){
return get(root, (Comparable) key);
}
// This helper method retrieves the value associated with the
// specified key in the tree rooted at "r".
@SuppressWarnings("unchecked")
private V get(AVLNode r, Comparable key){
if(r == null) {
return null;
}
int compare = key.compareTo(r.key);
if(compare == 0) {
return (V) r.value;
} else if(compare < 0) {
return get(r.left, key);
} else { // compare > 0
return get(r.right, key);
}
}
/**
* Returns true if the current map contains a mapping for the
* specified key.
*
* @param key The key whose presence in the map is being tested.
* @return If this map contains a mapping for the specified
* key.
*/
public boolean containsKey(Object key) {
return get((Comparable) key) != null;
}
/**
* Returns true if the current map contains no key-value mappings.
*
* @return If the current map contains no key-value mappings.
*/
public boolean isEmpty() {
return root == null;
}
/**
* Removes all of the mappings from the current map.
*/
public void clear() {
root = null;
numKeys = 0;
}
/**
* Returns the number of key-value mappings in this map
* @return The number of key-value mappings in this map
*/
public int size(){
return numKeys;
}
/**
* Returns the String representation of this map.
*
* @return The String representation of this map.
*/
@Override
public String toString() {
return "(" + subtreeToString(root) + ")";
}
// This helper method returns a String representation of the contents
// of the map for (sub-)tree with root "r".
private String subtreeToString(AVLNode r) {
String str = "";
if(r == null) {
return str;
}
str += r.key + ":" + r.value;
str += " (" + subtreeToString(r.left) + ") (" +
subtreeToString(r.right) + ")";
return str;
}
// This inner class creates each of the node(s) that
// compose the AVL tree structure.
class AVLNode<K, V> {
/**
* The key stored in the node.
*/
public K key;
/**
* The corresponding value associated with a key in the node.
*/
public V value;
/**
* The node to the left of "this" node.
*/
public AVLNode left;
/**
* The node to the right of "this" node.
*/
public AVLNode right;
/**
* The height of "this" node.
*/
public int height;
/**
* Constructs the AVLNode object (four parameters).
*
* @param key The key to be stored in the node.
* @param value The corresponding value to be stored in the node.
* @param left The node to the left of "this" node.
* @param right The node to the right of "this" node.
*/
@SuppressWarnings("unchecked")
public AVLNode(Object key, Object value, AVLNode left, AVLNode right) {
// bind to references
this.key = (K) key;
this.value = (V) value;
this.left = left;
this.right = right;
height = 0;
}
/**
* Constructs the AVLNode (two parameters).
*
* @param key The key to be stored in the node.
* @param value The corresponding value to be stored in the node.
*/
public AVLNode(Object key, Object value) {
// call three parameter constructor
this(key, value, null, null);
height = 0;
}
}
}
这是它实现的界面：
public interface BasicMap<K, V> {
/**
* Associates the specified value with the specified
* key in the current map. Neither key nor value should
* be <tt>null</tt>.
* @param key The key with which the specified value
* is to be associated.
* @param value The value to be associated with the
* specified key.
*/
public void put(K key, V value);
/**
* Returns the value to which the specified key is mapped,
* or <tt>null</tt> if the specified key is not mapped.
* @param key The key whose associated value is to be returned
* @return The value to which the specified key is mapped,
* or <tt>null</tt> if the specified key is not mapped.
*/
public V get(Object key);
/**
* Returns true if the current map contains a mapping for the
* specified key.
* @param key The key whose presence in the map is being tested.
* @return true if this map contains a mapping for the specified
* key.
*/
public boolean containsKey(Object key);
/**
* Returns true if the current map contains no key-value mappings.
* @return true if the current map contains no key-value mappings.
*/
public boolean isEmpty();
/**
* Removes all of the mappings from the current map.
*/
public void clear();
/**
* Returns the number of key-value mappings in this map
* @return The number of key-value mappings in this map
*/
public int size();
/**
* Returns the String representation of this map
* @return The String representation of this map
*/
public String toString();
}
答案 0 :(得分：0)
Fastutils中有这些数据结构的超酷实现，例如见课Double2FloatAVLTreeMap。
图书馆是开源的，所以也许你想学习那些代码（这些年后仍然感兴趣）。