7 二叉树的操作 四种遍历

package com.wwj.cn;

public interface TreeInterf {
    void PreOrderTraverse(TreeNode treeNode);// 前序遍历 递归

    void InOrderTraverse(TreeNode treeNode);// 中序遍历 递归

    void PostOrderTraverse(TreeNode treeNode);// 后序遍历 递归

    void LevelIterator(TreeNode treeNode);// 层序遍历

}




package com.wwj.cn;

import java.util.LinkedList;

public class TreeOperation implements TreeInterf {

    @Override
    public void PreOrderTraverse(TreeNode treeNode) {
        // TODO Auto-generated method stub
        if (treeNode == null) {
            return;
        }
        System.out.println(treeNode.val);
        PreOrderTraverse(treeNode.leftchild);
        PreOrderTraverse(treeNode.rightchild);
    }

    @Override
    public void InOrderTraverse(TreeNode treeNode) {
        if (treeNode == null) {
            return;
        }
        InOrderTraverse(treeNode.leftchild);
        System.out.println(treeNode.val);
        InOrderTraverse(treeNode.rightchild);

    }

    @Override
    public void PostOrderTraverse(TreeNode treeNode) {
        if (treeNode == null) {
            return;
        }
        PostOrderTraverse(treeNode.leftchild);

        PostOrderTraverse(treeNode.rightchild);

        System.out.println(treeNode.val);

    }

    @Override
    public void LevelIterator(TreeNode treeNode) {// 利用队列
        if (treeNode == null) {
            return;
        }
        LinkedList<TreeNode> queue = new LinkedList<>();
        TreeNode currentNode = null;
        queue.offer(treeNode);
        while (!queue.isEmpty()) {
            currentNode = queue.poll();
            System.out.println(currentNode.val);

            if (currentNode.leftchild != null) {
                queue.offer(currentNode.leftchild);
            }

            if (currentNode.rightchild != null) {
                queue.offer(currentNode.rightchild);
            }

        }

    }

}