基于二分搜索树实现map

package structures.mapdemo;

public class BSTMap, V> implements Map {

    private class Node {
        public Node left, right;
        public K key;
        public V value;

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

        public Node() {
            this(null, null);
        }

        @Override
        public String toString() {
            return key + ":" + value;
        }
    }

    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) {
            node = new Node(key, value);
            size++;
            return node;
        }

        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 /*key.compareTo(node.key) = 0*/ {
            node.value = value;
        }

        return node;
    }

    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;
    }

    @Override
    public V remove(K key) {
        Node node = getNode(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);
            successor.right = removeMin(node.right);
            successor.left = node.left;
            node.left = node.right = null;
            return successor;
        }
    }

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

    private Node getNode(K key) {
        return getNode(root, key);
    }

    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 V get(K key) {
        Node node = getNode(key);
        return node == null ? null : node.value;
    }

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

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

    @Override
    public boolean contains(K key) {
        return contains(root, key);
    }

    private boolean contains(Node node, K key) {

        if (node == null) {
            return false;
        }

        if (key.compareTo(node.key) == 0) {
            return true;
        } else if (key.compareTo(node.key) < 0) {
            return contains(node.left, key);
        } else  /*(key.compareTo(node.key) > 0)*/ {
            return contains(node.right, key);
        }
    }

    public void inOrder() {
        inOrder(root);
    }

    private void inOrder(Node node) {
        if (node == null) {
            return;
        }

        inOrder(node.left);
        System.out.println(node.key + ":" + node.value);
        inOrder(node.right);
    }
}