二分搜索树实现Java的Map(下)

二分搜索树Map

public class BSTMap<K extends Comparable<K>,V> implements Map<K,V> {

    private class Node
    {
        public K key;

        public V value;

        public Node left,right;

        public Node(K key,V value)
        {
            this.key = key;
            this.value = value;
            left = null;
            right = null;
        }
    }

    private Node root;

    private int size;

    public BSTMap()
    {
        root = null;
        size = 0;
    }
    @Override
    public void add(K key, V value) {
        root = add(root,key,value);
    }

    private Node add(Node node,K key,V value)
    {
        if (node == null)
        {
            size ++;
            return new Node(key,value);
        }
        if (key.compareTo(node.key) < 0)
        {
            node.left = add(node.left,key,value);
        }else if(key.compareTo(node.key) > 0)
        {
            node.right = add(node.right,key,value);
        }else {
            node.value = value;
        }
        return node;
    }

    @Override
    public V remove(K key) {
        Node node = getNode(root,key);
        if (node != null){
            root = remove(root,key);
            return node.value;
        }
        return null;
    }

    private Node remove(Node node,K key)
    {
        if (node == null)
        {
            return null;
        }
        if (key.compareTo(node.key) < 0)
        {
            node.left = remove(node.left,key);
            return node;
        }else if(key.compareTo(node.key) > 0)
        {
            node.right = remove(node.right,key);
            return node;
        }else {
            if (node.left == null)
            {
                Node rightNode = node.right;
                node.right = null;
                size--;
                return rightNode;
            }

            if (node.right == null)
            {
                Node leftNode = node.left;
                node.left = null;
                size--;
                return leftNode;
            }

            Node successor = minimum(node.right);
            successor.right = removeMin(node.right);
            node.left = node.right = null;
            return successor;
        }
    }

    private Node getNode(Node node,K key)
    {
        if (node == null)
        {
            return null;
        }
        if (key.compareTo(node.key) == 0)
        {
            return node;
        }else if (key.compareTo(node.key) < 0)
        {
            return getNode(node.left,key);
        }else {
            return getNode(node.right,key);
        }
    }

    @Override
    public boolean contains(K key) {
        return getNode(root,key) != null;
    }

    @Override
    public V get(K key) {
        Node node = getNode(root,key);
        return node == null ? null : node.value;
    }

    @Override
    public void set(K key, V newValue) {
        Node node = getNode(root,key);
        if (node == null)
        {
            throw new IllegalArgumentException( key + " is not exist");
        }
        node.value = newValue;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    private Node minimum(Node node)
    {
        if (node.left == null)
        {
            return node;
        }
        return minimum(node.left);
    }

    private Node removeMin(Node node)
    {
        if (node.left == null)
        {
            Node rightNode = node.right;
            node.right = null;
            size --;
            return rightNode;
        }
        node.left = removeMin(node.left);
        return node;
    }

}