------------------------AVL树--------------------------
自平衡树:AVL树是一颗二分搜索树,同时左右子树的高度差不超过1,AVL是自平衡的
主要是通过左旋和右旋来维护平衡
统计一本书中共出现多少个单词,每个单词出现了多少次:使用AVL树实现Set和Map,Set用于统计共出现了多少个不同的单词,Map用于容纳每个单词出现的次数。
AVLTree实现如下:
package avl; import java.util.ArrayList; public class AVLTree<K extends Comparable<K>, V> { private class Node{ public K key; public V value; public Node left, right; public int height; public Node(K key, V value){ this.key = key; this.value = value; left = null; right = null; height = 1; } } private Node root; private int size; public AVLTree(){ root = null; size = 0; } public int getSize(){ return size; } public boolean isEmpty(){ return size == 0; } // 判断该二叉树是否是一棵二分搜索树 public boolean isBST(){ ArrayList<K> keys = new ArrayList<>(); inOrder(root, keys); for(int i = 1 ; i < keys.size() ; i ++) if(keys.get(i - 1).compareTo(keys.get(i)) > 0) return false; return true; } private void inOrder(Node node, ArrayList<K> keys){ if(node == null) return; inOrder(node.left, keys); keys.add(node.key); inOrder(node.right, keys); } // 判断该二叉树是否是一棵平衡二叉树 public boolean isBalanced(){ return isBalanced(root); } // 判断以Node为根的二叉树是否是一棵平衡二叉树,递归算法 private boolean isBalanced(Node node){ if(node == null) return true; int balanceFactor = getBalanceFactor(node); if(Math.abs(balanceFactor) > 1) return false; return isBalanced(node.left) && isBalanced(node.right); } // 获得节点node的高度 private int getHeight(Node node){ if(node == null) return 0; return node.height; } // 获得节点node的平衡因子 private int getBalanceFactor(Node node){ if(node == null) return 0; return getHeight(node.left) - getHeight(node.right); } // 对节点y进行向右旋转操作,返回旋转后新的根节点x // y x // / \ / \ // x T4 向右旋转 (y) z y // / \ - - - - - - - -> / \ / \ // z T3 T1 T2 T3 T4 // / \ // T1 T2 private Node rightRotate(Node y) { Node x = y.left; Node T3 = x.right; // 向右旋转过程 x.right = y; y.left = T3; // 更新height y.height = Math.max(getHeight(y.left), getHeight(y.right)) + 1; x.height = Math.max(getHeight(x.left), getHeight(x.right)) + 1; return x; } // 对节点y进行向左旋转操作,返回旋转后新的根节点x // y x // / \ / \ // T1 x 向左旋转 (y) y z // / \ - - - - - - - -> / \ / \ // T2 z T1 T2 T3 T4 // / \ // T3 T4 private Node leftRotate(Node y) { Node x = y.right; Node T2 = x.left; // 向左旋转过程 x.left = y; y.right = T2; // 更新height y.height = Math.max(getHeight(y.left), getHeight(y.right)) + 1; x.height = Math.max(getHeight(x.left), getHeight(x.right)) + 1; return x; } // 向二分搜索树中添加新的元素(key, value) public void add(K key, V value){ root = add(root, key, value); } // 向以node为根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 // key.compareTo(node.key) == 0 node.value = value; // 更新height node.height = 1 + Math.max(getHeight(node.left), getHeight(node.right)); // 计算平衡因子 int balanceFactor = getBalanceFactor(node); // 平衡维护 // LL if (balanceFactor > 1 && getBalanceFactor(node.left) >= 0) return rightRotate(node); // RR if (balanceFactor < -1 && getBalanceFactor(node.right) <= 0) return leftRotate(node); // LR if (balanceFactor > 1 && getBalanceFactor(node.left) < 0) { node.left = leftRotate(node.left); return rightRotate(node); } // RL if (balanceFactor < -1 && getBalanceFactor(node.right) > 0) { node.right = rightRotate(node.right); return leftRotate(node); } 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(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); } public boolean contains(K key){ return getNode(root, key) != null; } public V get(K key){ Node node = getNode(root, key); return node == null ? null : node.value; } 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; } // 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); } // 从二分搜索树中删除键为key的节点 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; Node retNode; if( key.compareTo(node.key) < 0 ){ node.left = remove(node.left , key); // return node; retNode = node; } else if(key.compareTo(node.key) > 0 ){ node.right = remove(node.right, key); // return node; retNode = node; } else{ // key.compareTo(node.key) == 0 // 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; retNode = rightNode; } // 待删除节点右子树为空的情况 else if(node.right == null){ Node leftNode = node.left; node.left = null; size --; // return leftNode; retNode = leftNode; } // 待删除节点左右子树均不为空的情况 else{ // 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.right = remove(node.right, successor.key); successor.left = node.left; node.left = node.right = null; // return successor; retNode = successor; } } if(retNode == null) return null; // 更新height retNode.height = 1 + Math.max(getHeight(retNode.left), getHeight(retNode.right)); // 计算平衡因子 int balanceFactor = getBalanceFactor(retNode); // 平衡维护 // LL if (balanceFactor > 1 && getBalanceFactor(retNode.left) >= 0) return rightRotate(retNode); // RR if (balanceFactor < -1 && getBalanceFactor(retNode.right) <= 0) return leftRotate(retNode); // LR if (balanceFactor > 1 && getBalanceFactor(retNode.left) < 0) { retNode.left = leftRotate(retNode.left); return rightRotate(retNode); } // RL if (balanceFactor < -1 && getBalanceFactor(retNode.right) > 0) { retNode.right = rightRotate(retNode.right); return leftRotate(retNode); } return retNode; } }
AVLSet实现如下:
package avl; public class AVLSet<E extends Comparable<E>> implements Set<E> { private AVLTree<E, Object> avl; public AVLSet(){ avl = new AVLTree<>(); } @Override public int getSize(){ return avl.getSize(); } @Override public boolean isEmpty(){ return avl.isEmpty(); } @Override public void add(E e){ avl.add(e, null); } @Override public boolean contains(E e){ return avl.contains(e); } @Override public void remove(E e){ avl.remove(e); } }
AVLMap实现如下:
package avl; public class AVLMap<K extends Comparable<K>, V> implements Map<K, V> { private AVLTree<K, V> avl; public AVLMap(){ avl = new AVLTree<>(); } @Override public int getSize(){ return avl.getSize(); } @Override public boolean isEmpty(){ return avl.isEmpty(); } @Override public void add(K key, V value){ avl.add(key, value); } @Override public boolean contains(K key){ return avl.contains(key); } @Override public V get(K key){ return avl.get(key); } @Override public void set(K key, V newValue){ avl.set(key, newValue); } @Override public V remove(K key){ return avl.remove(key); } }
原文地址:https://www.cnblogs.com/xiao1572662/p/12128289.html
时间: 2024-11-09 02:51:19