二叉树的学习创建以及遍历方式

先创建一个结点类

package Igorithm.day7_NiXu.main;

public class Tree {
	private String weight;
	private int index;//节点下标
	private Tree leftChild;
	private Tree rightChild;
	private Tree parent;
	
	
	public Tree() {
		
	}
	
	public Tree(int index, String data){
      this.index = index;
      this.weight = data;
      this.leftChild = null;
      this.rightChild = null;
	}
	public Tree(String weight, int index, Tree leftChild, Tree rightChild, Tree parent) {
		
		this.weight = weight;
		this.index = index;
		this.leftChild = leftChild;
		this.rightChild = rightChild;
		this.parent = parent;
	}
	
	public int getIndex() {
		return index;
	}
	public void setIndex(int index) {
		this.index = index;
	}
	public String getWeight() {
		return weight;
	}
	public void setWeight(String weight) {
		this.weight = weight;
	}
	public Tree getLeftChild() {
		return leftChild;
	}
	public void setLeftChild(Tree leftChild) {
		this.leftChild = leftChild;
	}
	public Tree getRightChild() {
		return rightChild;
	}
	public void setRightChild(Tree rightChild) {
		this.rightChild = rightChild;
	}
	public Tree getParent() {
		return parent;
	}
	public void setParent(Tree parent) {
		this.parent = parent;
	}
	
	
}

在写二叉树：注我写的有缺陷，如果是单节点会默认作为左子树

package Igorithm.day7_NiXu.main;

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

public class BinaryTrees {
	private Tree root = new Tree();
	private List<Tree> list = new ArrayList<Tree>();
	
	
	public BinaryTrees() {
		root.setIndex(0);
		list.add(root);
	}


	public BinaryTrees(Tree root, List<Tree> list) {
		this.root = root;
		this.list = list;
	}
	
	/**
	 * 总体思路：从头结点开始遍历
	  *  当结点权值第一次为 0 时，创建一个新结点作为左子树
	  *  当结点权值第一次不为 0 时创建一个结点作为左叶子结点
	  *  当结点权值第二次不为 0 时创建一个结点作为右叶子结点
	  *  当结点权值超过两次不为 0 时，index递减 ，并且为上一个结点创建一个结点作为右叶子结点
	  *  当结点返回到了根节点时，要注意index的值，因为此时我要为期创建右节点
	  *                  且会用到list集合中的最后一个，index = list.size-1而不是index++（第二个）
	  *                  我们其实大多数都是在对list集合中最后一个元素做出操作
	  *                  只有在生成右子树时才会找list前面的元素
	  *  还有，当结点权值再次为 0 时， 取最后此时index对应下的list集合元素为其建立右子树
	  *  。
	 * @param ls
	 * @return 在list集合中第一个元素就代表这我们要生成的二叉树
	 */
	public Tree createBinaryTree(List ls) {
		boolean flag =false;
		int index = 0;//记录最近插入的非叶子结点在list中的位置
		for(int i = 1,k=0; i < ls.size();i++) {
			String treeNum = (String) ls.get(i);
			if (flag && k==0) {
				index = list.size()-1;
			}
			Tree remove = (Tree) list.remove(index);
			Tree tree = new Tree();
			tree.setParent(remove);
			if ("0".equals(treeNum)) {
				k=0;
				tree.setIndex(index+1);
				if (!flag) {
					
					remove.setLeftChild(tree);
				}else {
					remove.setRightChild(tree);
				}
				list.add(index,remove);
				index++;
			}
			else if (k==0) {
				tree.setWeight(treeNum);
				remove.setLeftChild(tree);
				list.add(index,remove);
				k++;
			}else {
				tree.setWeight(treeNum);
				remove.setRightChild(tree);
				list.add(index,remove);
				index--;
				flag =true;
				k++;
			}
			list.add(tree);
		}
		return list.get(0);
		
	}
	
	public static void main(String[] args) {
		BinaryTrees binaryTrees = new BinaryTrees();
		List<String> list = new ArrayList<>();
		String str[] = new String[] {"0","0","0","2","1","5","0","3","0","6","8"};
		Collections.addAll(list, str);
		Tree createBinaryTree = binaryTrees.createBinaryTree(list);
		show1(createBinaryTree);
		System.out.println("______________");
		show2(createBinaryTree);
		System.out.println("______________");
		show3(createBinaryTree);
	}
	
	

	/**
	  *   递归：先序遍历
	 * @param tree
	 */
	public static void show1(Tree tree) {
		if (tree!=null) {
			if (tree.getWeight()!=null) {
				System.out.println(tree.getWeight());
			}
			show1(tree.getLeftChild());
			show1(tree.getRightChild());
		}
	}
	/**
	  *   递归：中序遍历
	 * @param tree
	 */
	public static void show2(Tree tree) {
		if (tree!=null) {
			show2(tree.getLeftChild());
			if (tree.getWeight()!=null) {
				System.out.println(tree.getWeight());
			}
			show2(tree.getRightChild());
		}
	}
	
	/**
	  *   递归：后序遍历
	 * @param tree
	 */
	public static void show3(Tree tree) {
		if (tree!=null) {
			show3(tree.getLeftChild());
			show3(tree.getRightChild());
			if (tree.getWeight()!=null) {
				System.out.println(tree.getWeight());
			}
		}
	}

}