BSTMap.java

package map;

import set.FileOperation;

import java.util.ArrayList;

/**
 *  映射 Map
 *  1）、存储 Key：value 数据对的数据结构。
 *  2）、根据 Key，寻找 Value。
 *
 *  非常容易使用链表或者二分搜索树来实现。
 *                                  LinkedListMap  BSTMap   平均     最差
 *  add、remove、set、get、contains     O(n)          O(h)   O(logn)  O(n)
 */
public class BSTMap<K extends Comparable<K>, V> implements Map<K, V> {

    private class Node {

        private K key;
        private V value;
        private Node left;
        private Node right;

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

    private Node root;
    private int size;

    public BSTMap() {
        this.root = null;
        this.size = 0;
    }

    // 向二分搜索树中添加新的元素（key，value）
    @Override
    public void add(K key, V value) {
        root = add(root, key, value);
    }

    // 向以 Node 为根节点的二分搜索树中插入元素（key，value），递归算法
    // 返回插入新节点后二分搜索树的根
    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;
    }

    // 返回以 Node 为根节点的二分搜索树中，key 所在的节点
    private Node getNode(Node node, K key) {

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

        if (node.key.equals(key)) {
            return node;
        } else if (key.compareTo(node.key) < 0) {
            return getNode(node.left, key);
        } else {
            return getNode(node.right, key);
        }
    }

    // 从二分搜索树中删除键为 key 的节点
    @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 {

            // 待删除节点左子树为空的情况
            if (node.left == null) {
                Node rightNode = node.right;
                node.right = null;
                size --;
                return rightNode;
            }

            // 待删除节点右子树为空的情况
            if (node.right == null) {
                Node leftNode = node.left;
                node.left = null;
                size --;
                return leftNode;
            }

            // 待删除节点左右子树都为空的情况
            // 找到比待删除节点大的最小节点，即待删除节点右子树的最小节点
            // 用这个节点顶替待删除节点的位置
            Node successor = minimum(node.right);
            successor.right = removeMin(node.right);
            successor.left = node.left;

            node.left = node.right = null;

            return successor;
        }
    }

    // 返回以 Node 为根的二分搜索树的最小值所在的节点
    private Node minimum(Node node) {
        if (node.left == null) {
            return node;
        }
        return minimum(node.left);
    }

    // 删除掉以 Node 为根的二分搜索树中的最小节点
    // 返回删除节点后新的二分搜索树的根
    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 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 + " on exist~");
        }

        node.value = newValue;
    }

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

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

    public static void main(String[] args){

        System.out.println("Pride and Prejudice");

        ArrayList<String> words = new ArrayList<>();
        if(FileOperation.readFile("pride-and-prejudice.txt", words)) {
            System.out.println("Total words: " + words.size());

            BSTMap<String, Integer> map = new BSTMap<>();
            for (String word : words) {
                if (map.contains(word))
                    map.set(word, map.get(word) + 1);
                else
                    map.add(word, 1);
            }

            System.out.println("Total different words: " + map.getSize());
            System.out.println("Frequency of PRIDE: " + map.get("pride"));
            System.out.println("Frequency of PREJUDICE: " + map.get("prejudice"));
        }

        System.out.println();
    }


}