【code】java创建哈夫曼树和实现哈夫曼编码

创建哈夫曼树

主要思想：

(1)对List集合中所有节点进行排序。

(2)找出List集合中权值最小的两个节点。

(3)以权值最小的两个节点作为子节点创建新节点。

(4)从List集合中删除权值最小的两个节点，将新节点添加到List集合中。

import java.util.*;public class HuffmanTree{public static class Node<E>{E data;double weight;Node leftChild;Node rightChild;public Node(E data , double weight){this.data = data;this.weight = weight;}public String toString(){return "Node[data=" + data+ ", weight=" + weight + "]";}}public static void main(String[] args){List<Node> nodes = new ArrayList<Node>();nodes.add(new Node("A" , 40.0));nodes.add(new Node("B" , 8.0));nodes.add(new Node("C" , 10.0));nodes.add(new Node("D" , 30.0));nodes.add(new Node("E" , 10.0));nodes.add(new Node("F" , 2.0));Node root = HuffmanTree.createTree(nodes);System.out.println(breadthFirst(root));}/** * 构造哈夫曼树 * @param nodes 节点集合 * @return 构造出来的哈夫曼树的根节点 */private static Node createTree(List<Node> nodes){//只要nodes数组中还有2个以上的节点while (nodes.size() > 1){quickSort(nodes);//获取权值最小的两个节点Node left = nodes.get(nodes.size() - 1);Node right = nodes.get(nodes.size() - 2);//生成新节点，新节点的权值为两个子节点的权值之和Node parent = new Node(null , left.weight + right.weight);//让新节点作为权值最小的两个节点的父节点parent.leftChild = left;parent.rightChild = right;//删除权值最小的两个节点nodes.remove(nodes.size() - 1);nodes.remove(nodes.size() - 1);//将新生成的父节点添加到集合中nodes.add(parent);}//返回nodes集合中唯一的节点，也就是根节点return nodes.get(0);}//将指定数组的i和j索引处的元素交换private static void swap(List<Node> nodes, int i, int j){Node tmp;tmp = nodes.get(i);nodes.set(i , nodes.get(j));nodes.set(j , tmp);}//实现快速排序算法，用于对节点进行排序。从大到小的排序private static void subSort(List<Node> nodes, int start , int end){//需要排序if (start < end){//以第一个元素作为分界值Node base = nodes.get(start);//i从左边搜索，搜索大于分界值的元素的索引int i = start;//j从右边开始搜索，搜索小于分界值的元素的索引int j = end + 1;while(true){//找到大于分界值的元素的索引，或i已经到了end处while(i < end && nodes.get(++i).weight >= base.weight);//找到小于分界值的元素的索引，或j已经到了start处while(j > start && nodes.get(--j).weight <= base.weight);if (i < j){swap(nodes , i , j);}else{break;}}swap(nodes , start , j);//递归左子序列subSort(nodes , start , j - 1);//递归右边子序列subSort(nodes , j + 1, end);}}public static void quickSort(List<Node> nodes) {subSort(nodes , 0 , nodes.size() - 1);}//广度优先遍历public static List<Node> breadthFirst(Node root){Queue<Node> queue = new ArrayDeque<Node>();List<Node> list = new ArrayList<Node>();if( root != null){//将根元素入“队列”queue.offer(root);}while(!queue.isEmpty()){//将该队列的“队尾”的元素添加到List中list.add(queue.peek());Node p = queue.poll();//如果左子节点不为null，将它加入“队列”if(p.leftChild != null){queue.offer(p.leftChild);}//如果右子节点不为null，将它加入“队列”if(p.rightChild != null){queue.offer(p.rightChild);}}return list;}}

 哈夫曼编码

规律：假如有N个叶子节点需要编码，最终得到的哈夫曼树一定有N层，哈夫曼编码得到的二进制码的最大长度为N-1。

import java.util.ArrayDeque;import java.util.ArrayList;import java.util.Collections;import java.util.HashSet;import java.util.List;import java.util.Queue;import java.util.Scanner;public class HuffmanCoding {public static String writeString;public static class HNode {String data = "";String coding = "";@Overridepublic String toString() {return "HNode [coding=" + coding + ", data=" + data + "]";}public HNode(String data) {super();this.data = data;}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + ((data == null) ? 0 : data.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;HNode other = (HNode) obj;if (data == null) {if (other.data != null)return false;} else if (!data.equals(other.data))return false;return true;}}public static class Node {HNode data;int weight;Node leftChild;Node rightChild;public Node(HNode data, int weight) {this.data = data;this.weight = weight;}public String toString() {return "Node[data=" + data + ", weight=" + weight + "]";}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + ((data == null) ? 0 : data.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Node other = (Node) obj;if (data == null) {if (other.data != null)return false;} else if (!data.equals(other.data))return false;return true;}}public static void main(String[] args) {System.out.println("请输入字符串：");Scanner scanner = new Scanner(System.in);HuffmanCoding.writeString = scanner.nextLine();char[] chars = writeString.toCharArray();List<Node> nodes = new ArrayList<Node>();for (int i = 0; i < chars.length; i++) {Node t = new Node(new HNode(String.valueOf(chars[i])), 1);if (nodes.contains(t)) {nodes.get(nodes.indexOf(t)).weight++;} else {nodes.add(t);}}// System.out.println(nodes);Node root = HuffmanCoding.createTree(nodes);breadthFirst(root, nodes);for (int i = 0; i < chars.length; i++) {Node t = new Node(new HNode(String.valueOf(chars[i])), 1);System.out.print(nodes.get(nodes.indexOf(t)).data.coding);}}private static Node createTree(List<Node> nodess) {List<Node> nodes = new ArrayList<Node>(nodess);// 只要nodes数组中还有2个以上的节点while (nodes.size() > 1) {quickSort(nodes);// 获取权值最小的两个节点Node left = nodes.get(nodes.size() - 1);Node right = nodes.get(nodes.size() - 2);// 生成新节点，新节点的权值为两个子节点的权值之和Node parent = new Node(new HNode(null), left.weight + right.weight);// 让新节点作为权值最小的两个节点的父节点parent.leftChild = left;parent.rightChild = right;// 删除权值最小的两个节点nodes.remove(nodes.size() - 1);nodes.remove(nodes.size() - 1);// 将新生成的父节点添加到集合中nodes.add(parent);}// 返回nodes集合中唯一的节点，也就是根节点return nodes.get(0);}public static void quickSort(List<Node> nodes) {subSort(nodes, 0, nodes.size() - 1);}private static void subSort(List<Node> nodes, int start, int end) {if (start < end) {Node base = nodes.get(start);int i = start;int j = end + 1;while (true) {while (i < end && nodes.get(++i).weight >= base.weight);while (j > start && nodes.get(--j).weight <= base.weight);if (i < j) {swap(nodes, i, j);} else {break;}}swap(nodes, start, j);// 递归左子序列subSort(nodes, start, j - 1);// 递归右边子序列subSort(nodes, j + 1, end);}}private static void swap(List<Node> nodes, int i, int j) {Node tmp;tmp = nodes.get(i);nodes.set(i, nodes.get(j));nodes.set(j, tmp);}// 广度优先遍历public static void breadthFirst(Node root, List<Node> nodes) {// System.out.println("我  "+nodes);Queue<Node> queue = new ArrayDeque<Node>();List<Node> list = new ArrayList<Node>();if (root != null) {// 将根元素入“队列”queue.offer(root);}while (!queue.isEmpty()) {// 将该队列的“队尾”的元素添加到List中list.add(queue.peek());Node p = queue.poll();// 如果左子节点不为null，将它加入“队列”if (p.leftChild != null) {queue.offer(p.leftChild);p.leftChild.data.coding = p.data.coding + "0";} else {// System.out.println(p+" "+p.data+" "+p.data.data+// " "+p.data.coding);// System.out.println("nodes.indexOf(p)"+nodes.contains(p));((Node) nodes.get(nodes.indexOf(p))).data.coding = p.data.coding;}// 如果右子节点不为null，将它加入“队列”if (p.rightChild != null) {queue.offer(p.rightChild);p.rightChild.data.coding = p.data.coding + "1";}// else {// nodes.get(nodes.indexOf(p)).data.coding=p.data.coding;// System.out.println("you "+p.data.coding);// }}}}