哈夫曼树与哈夫曼编码

思路：哈夫曼编码

代码：

import java.util.Scanner;import java.util.HashMap;import java.util.Map;import java.util.PriorityQueue;//知识点1: 树节点，自定义比较规则class Node implements Comparable<Node>{    public int val;    public Node left;    public Node right;    Node(int val){        this.val = val;    }    @Override    public int compareTo(Node o) {        return this.val-o.val;    }}public class Main{        public static void main(String[] args){            Scanner sc = new Scanner(System.in);            while(sc.hasNext()){                String str = sc.nextLine().trim();                //知识点2: Map计数统计                Map<Character, Integer> map = new HashMap<Character, Integer>();                for(int i=0; i<str.length(); i++){                    char ch = str.charAt(i);                    if(map.containsKey(ch)){                        int val = map.get(ch);                        map.put(ch, ++val);                    }else{                        map.put(ch, 1);                    }                }                //知识点3: 优先队列的使用！！！（最重要的知识点）                PriorityQueue<Node> queue = new PriorityQueue<Node>();                for(char ch : map.keySet()){                    Node node = new Node(map.get(ch));                    queue.offer(node);                }                //知识点4: 哈夫曼编码                while(queue.size()>1){                    Node node1 = queue.poll();                    Node node2 = queue.poll();                    Node nodeNew = new Node(node1.val+node2.val);                    nodeNew.left = node1;                    nodeNew.right = node2;                    queue.offer(nodeNew);                }                Node root = queue.poll();                System.out.println(countLength(root, 0));            }        }        //知识点5: 统计编码长度        public static int countLength(Node node, int level){            if(node.left==null && node.right==null){                return node.val*level;            }            return countLength(node.left, level+1)+countLength(node.right, level+1);        }}