算法与数据结构系列之[红黑树-下]

上篇介绍了红黑树的概述，这篇贴出红黑树的java实现代码。

public class RBTree<K extends Comparable<K>, V>{

    private static final boolean RED = true;
    private static final boolean BLACK = false;

    private class Node{
        public K key;
        public V value;
        public Node left, right;
        public boolean color; //红黑树颜色区别

        public Node(K key, V value){
            this.key = key;
            this.value = value;
            left = null;
            right = null;
            color = RED;  //插入节点时，总是先和另一节点融合，所以初始时设置为红色
        }
    }

    private Node root;
    private int size;

    public RBTree(){
        root = null;
        size = 0;
    }

    //获取元素个数
    public int getSize(){
        return size;
    }

    //判断红黑树是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //判断节点的颜色是否为红色
    private boolean isRed(Node node){
        return node.color == RED;
    }

    //左旋转
    private Node leftRotate(Node node){
        Node x = node.right;
        node.right = x.left;
        x.left = node;
        x.color = node.color;
        node.color = RED;
        return node;
    }

    //颜色翻转
    private void flipColors(Node node){
        node.color = RED;
        node.left.color = BLACK;
        node.right.color = BLACK;
    }

    //右旋转
    private Node rightRotate(Node node){
        Node x  = node.left;
        //右旋转
        x.right = node;
        node.left = x.right;
        x.color = node.color;
        node.color = RED;
        return  x;
    }

    // 向红黑树中添加新的元素(key, value)
    public void add(K key, V value){
        root = add(root, key, value);
        root.color = BLACK;   //最终的根节点为黑色的
    }

    // 向以node为根的红黑树中插入元素(key, value)，递归算法
    // 返回插入新节点后二红黑树的根
    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 // key.compareTo(node.key) == 0
            node.value = value;

        if(isRed(node.right) && !isRed(node.left))
            node = leftRotate(node);
        if(isRed(node.left) && isRed(node.left.left))
            node = rightRotate(node);
        if(isRed(node.left) && isRed(node.right))
            flipColors(node);

        return node;
    }

    // 返回以node为根节点的红黑树中，key所在的节点
    private Node getNode(Node node, K key){

        if(node == null)
            return null;

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

    //判断红黑树中是否包含key
    public boolean contains(K key){
        return getNode(root, key) != null;
    }

    //获取红黑树键为key的值value
    public V get(K key){

        Node node = getNode(root, key);
        return node == null ? null : node.value;
    }

    //将红黑树键为key的value值设置成新的newValue值
    public void set(K key, V newValue){
        Node node = getNode(root, key);
        if(node == null)
            throw new IllegalArgumentException(key + " doesn't exist!");

        node.value = newValue;
    }
}

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