从零开始学数据结构和算法(七)-huffman-树与-AVL-树，高级工程师致全国移动互联网工作者的一封信

• 左旋

• 右旋

代码

Huffman 树

public class HuffmanTree {
TreeNode root;
public TreeNode createHuffManTree(ArrayList list) {
while (list.size() > 1) {
Collections.sort(list);
TreeNode left = list.get(list.size() - 1);
TreeNode right = list.get(list.size() - 2);
TreeNode parent = new TreeNode(“p”, left.weight + right.weight);
parent.leftChild = left;
left.parent = parent;
parent.rightChild = right;
right.parent = parent;
list.remove(left);
list.remove(right);
list.add(parent);
}
root = list.get(0);
return list.get(0);
}

public void showHuffman(TreeNode root) {
LinkedList list = new LinkedList<>();
list.offer(root);//入队
while (!list.isEmpty()) {
TreeNode node = list.pop();
System.out.println(node.data);
if (node.leftChild != null) {
list.offer(node.leftChild);
}
if (node.rightChild != null) {
list.offer(node.rightChild);
}
}
}

@Test
public void test() {
ArrayList list = new ArrayList<>();
TreeNode node = new TreeNode(“good”, 50);
list.add(node);
list.add(new TreeNode(“morning”, 10));
TreeNode node2 =new TreeNode(“afternoon”, 20);
list.add(node2);
list.add(new TreeNode(“hell”, 110));
list.add(new TreeNode(“hi”, 200));
HuffmanTree tree = new HuffmanTree();
tree.createHuffManTree(list);
tree.showHuffman(tree.root);
getCode(node2);
}

/**

• 编码
  */
  public void getCode(TreeNode node) {
  TreeNode tNode = node;
  Stack stack = new Stack<>();
  while (tNode != null && tNode.parent != null) {
  //left 0 right 1
  if (tNode.parent.leftChild == tNode) {
  stack.push(“0”);
  } else if (tNode.parent.rightChild == tNode) {
  stack.push(“1”);
  }
  tNode = tNode.parent;
  }
  System.out.println();
  while (!stack.isEmpty()) {
  System.out.print(stack.pop());
  }
  }

/**

• 结点
• @param
  */
  public static class TreeNode implements Comparable<TreeNode> {
  T data;
  int weight;
  TreeNode leftChild;
  TreeNode rightChild;
  TreeNode parent;

public TreeNode(T data, int weight) {
this.data = data;
this.weight = weight;
leftChild = null;
rightChild = null;
parent = null;
}

@Override
public int compareTo(@NonNull Tree
Node o) {
if (this.weight > o.weight) {
return -1;
} else if (this.weight < o.weight) {
return 1;
}
return 0;
}
}
}

平衡二叉树

• 左旋转

public class AVLBTree<E extends Comparable> {
Node root;
int size;
public class Node<E extends Comparable>{
E element;
int balance=0;//平衡因子
Node left;
Node right;
Node parent;
public Node(E element,Node parent){
this.element=element;
this.parent=parent;
=0;//平衡因子
Node left;
Node right;
Node parent;
public Node(E element,Node parent){
this.element=element;
this.parent=parent;