赫夫曼树的创建

代码

public class Main {
    public static void main(String[] args) {
        int[] arr = {9,8,7};

        Node huffmanTree = createHuffmanTree(arr);
        huffmanTree.preList(huffmanTree);
//        List<Node> nodeList = new ArrayList<Node>();
//        for (int i = 0;i < arr.length;i++){
//            nodeList.add(new Node(arr[i]));
//        }
//        nodeList.remove(0);
//        System.out.println(nodeList.get(0));
    }

    public static Node createHuffmanTree(int[] arr){
        //首先 为了方便，先将arr中的每一个元素封装成一个节点，并装入集合中
        List<Node> nodeList = new ArrayList<Node>();
        for (int i = 0;i < arr.length;i++){
            nodeList.add(new Node(arr[i]));
        }

        //添加完了之后 对集合中元素进行排序
        Collections.sort(nodeList);
        System.out.println("nodeList1:"+nodeList);
        //当集合中元素大于1的时候就一直排，当等于1 的时候说明哈夫曼树创建完成
        while (nodeList.size() > 1){
            //首先取出两个权值最小的节点
            Node leftNode = nodeList.get(0);
            Node rightNode = nodeList.get(1);

            //然后创建这两个节点的父节点，并与之连接
            Node parent = new Node(leftNode.value + rightNode.value);
            parent.left = leftNode;
            parent.right = rightNode;
            System.out.println("leftNode:"+leftNode);
            System.out.println("rightNode:"+rightNode);
            //然后把刚取出来的这两个节点删除
            nodeList.remove(0);
            nodeList.remove(0);

            //或者用下面这两行
//            nodeList.remove(leftNode);
//            nodeList.remove(rightNode);
            System.out.println("afterRemove:"+nodeList);
            //把parent节点加进去 并重新排序
            nodeList.add(parent);

            Collections.sort(nodeList);
            System.out.println("nodeList:"+nodeList);
        }
        System.out.println(nodeList);
        return nodeList.get(0);
    }


}

//让Node进行排序
class Node implements Comparable<Node>{
    int value;
    Node left;
    Node right;

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

    @Override
    public String toString() {
        return "Node{" +
                "value=" + value +
                '}';
    }

    @Override
    public int compareTo(Node o) {
        return this.value - o.value;//从小到达排序
    }
    public void preList(Node root){
        if (root == null){
            System.out.println("为空");
            return;
        }else {
            this.preList();
        }
    }
    public void preList(){
        System.out.println(this);
        if (this.left != null){
            this.left.preList();
        }
        if (this.right != null){
            this.right.preList();
        }
    }

}

结果

nodeList1:[Node{value=7}, Node{value=8}, Node{value=9}]
leftNode:Node{value=7}
rightNode:Node{value=8}
afterRemove:[Node{value=9}]
nodeList:[Node{value=9}, Node{value=15}]
leftNode:Node{value=9}
rightNode:Node{value=15}
afterRemove:[]
nodeList:[Node{value=24}]
[Node{value=24}]
Node{value=24}
Node{value=9}
Node{value=15}
Node{value=7}
Node{value=8}

意外收获：​​ArrayList​​​的​​remove​​

​​ArrayList​​​的​​remove​​方法每调用一次，会将集合的索引值重置。比如元素为9，8，7.如果想删除9和8.可以

arrayList.remove(9);
arrayList.remove(8);

也可以

arrayList.remove(0);
arrayList.remove(0);

我们说第二种情况，为啥两次都是0，因为第一次删除之后，会将索引值重置，此时的0不再是删除了9之后指向的​​null​​，而是8.