数据结构之哈夫曼树（Huffman Tree）-Java实现

将一串数字转换为哈夫曼树的方法如下：首先把数组排序，每次取出两个最小数字节点，并将其组成一个新的二叉树，该二叉树的根是取出的两个节点的和，合并后将这两个节点移除，使用合并后的节点代替，再次排序，重复上述，即可得到WPL树。

代码实现如下

package 赫夫曼树;


public class HuffmanTreeNode implements Comparable {
    int value;
    HuffmanTreeNode leftNode;
    HuffmanTreeNode rightNode;

    public HuffmanTreeNode(int value) {
        this.value = value;
    }


    @Override
    public int compareTo(HuffmanTreeNode huffmanTreeNode) {
        return this.value - huffmanTreeNode.value;
    }
}

package 赫夫曼树;

import 二叉树.BinaryTreeNode;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;


public class GenerateHuffmanTree {

    public static HuffmanTreeNode HuffmanTree(int[] arr) {

        ArrayList arrayList = new ArrayList<>();
        for (int i = 0; i < arr.length; i++) {
            arrayList.add(new HuffmanTreeNode(arr[i]));
        }
        while (arrayList.size() > 1) {//只要数组大小不为1，就继续合并
            Collections.sort(arrayList);//首先进行排序

            HuffmanTreeNode small = arrayList.get(0);
            HuffmanTreeNode bigger = arrayList.get(1);//取出前两个最小的值

            HuffmanTreeNode sum = new HuffmanTreeNode(small.value + bigger.value);
            //创建一个新树节点，其值为二者之和，左树为较小的那一个，右树为较大的那一个
            sum.leftNode = small;
            sum.rightNode = bigger;

            arrayList.remove(small);
            arrayList.remove(bigger);//二者被合并后将其从数组中移除
            arrayList.add(sum);//添加合并后的树到数组

        }

        return arrayList.get(0);
    }

    public static void PreOrdered(HuffmanTreeNode root) {
        if (root != null) {
            System.out.print(root.value + " ");
            PreOrdered(root.leftNode);
            PreOrdered(root.rightNode);
        }

    }
}

public static void main(String[] args) {
        int[] arr = new int[]{3,8,7,2,5};
        HuffmanTreeNode huffmanTreeNode = GenerateHuffmanTree.HuffmanTree(arr);
        GenerateHuffmanTree.PreOrdered(huffmanTreeNode);
    }

结果：

67 29 38 15 7 8 23 10 4 1 3 6 13 
Process finished with exit code 0