伸展树 Splay Tree

最新推荐文章于 2022-03-10 10:46:43 发布

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最新推荐文章于 2022-03-10 10:46:43 发布

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分类专栏： algorithm 文章标签：伸展树

本文链接：https://blog.youkuaiyun.com/woshixiazaizhe/article/details/81670139

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本文介绍了伸展树的Java实现，包括节点定义、树的定义、插入节点和搜索操作。伸展树是一种特殊的二叉搜索树，每次访问的节点都会通过旋转变为根节点。

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在二叉搜索树的基础上加了每次访问的节点都会变为根节点

伸展树 JAVA 实现

1、节点定义

	private static class SplayTreeNode<T extends Comparable<T>> {
		private T element;
		private SplayTreeNode<T> leftNode;
		private SplayTreeNode<T> rightNode;

		public SplayTreeNode(T element, SplayTreeNode<T> leftNode, SplayTreeNode<T> rightNode) {
			this.element = element;
			this.leftNode = leftNode;
			this.rightNode = rightNode;
		}

		public SplayTreeNode(T element) {
			this(element, null, null);
		}

	}

2、树的定义

public class SplayTree<T extends Comparable<T>> {
	
	private SplayTreeNode<T> rootNode;    // 根节点
 
}

3、插入节点

	public void insert(T element) {
		if (element == null) {
			return;
		}
		rootNode = insert(element, rootNode);
	}
	
	private SplayTreeNode<T> insert(T element, SplayTreeNode<T> node) {
		if (node == null) {
			node = new SplayTreeNode<T>(element);
		}
		
		int compareResult = element.compareTo(node.element);
		if (compareResult < 0) {
			node.leftNode = insert(element, node.leftNode);
		} else if (compareResult > 0) {
			node.rightNode = insert(element, node.rightNode);
		}
		return node;
	}

4、搜索

	public T search(T element) {
		if (element == null) {
			return null;
		}
		rootNode = splay(element, rootNode);
		return rootNode.element;
	}
	
	/*
	 * 旋转key对应的节点为根节点，并返回根节点。
	 * 自低向上旋转
	 */
	private SplayTreeNode<T> splay(T element, SplayTreeNode<T> node) {
		if (node == null) {
			return null;
		}
		SplayTreeNode<T> left = null;
        SplayTreeNode<T> right = null;
		int compareResult = element.compareTo(node.element);
    	if (compareResult < 0) {
    		right = node;
    		if (node.leftNode != null) {
    			node = splay(element, node.leftNode);
    		}
    		right.leftNode = node.rightNode;
    		node.rightNode = right;
    	} else if (compareResult > 0) {
    		left = node;
    		if (node.rightNode != null) {
    			node = splay(element, node.rightNode);
    		}
    		left.rightNode = node.leftNode;
    		node.leftNode = left;
    	} else {
    	}
		return node;
	}