树的深度优先遍历和广度优先遍历非递归实现.

注:树的深度优先遍历就是二叉树的先序遍历.（我写的深度优先遍历可能有点奇怪，不是按照那种一次遍历到左子树的结点那种方式写的）

下面是我用java实现的代码.

package com.datastruct;

import java.util.LinkedList;
import java.util.Stack;

public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }
    
    
    /*
     *树的深度优先遍历 
     *按树的每一条分支遍历树
     *利用一个栈进行辅助
     */
    public void DeepFirstSearch_NoRecursion(TreeNode root)
    {
        Stack<TreeNode> treeStack = new Stack<>();
        
        if(root == null)
        {
            return;
        }
        
        treeStack.add(root);
        
        while(!treeStack.isEmpty())
        {
            TreeNode currentNode =  treeStack.pop();//栈顶元素出栈
            System.out.print(currentNode.val);//访问节点
            
            /*深搜需要先访问左子树的一条分支,故右孩子先入栈*/
            if(currentNode.right != null)
            {
                treeStack.push(currentNode.right);
            }
            
            if(currentNode.left != null)
            {
                treeStack.push(currentNode.left);
            }
        }
    }
    
    /*
     *广度优先遍历 
     *按照树的每一层进行遍历
     *利用一个队列进行辅助
     */
    public void BreadFirstSearch_NoRecursion(TreeNode root)
    {
        LinkedList<TreeNode> treeQueue = new LinkedList<>();//用链表来模拟队列
        
        if(root == null)
        {
            return;
        }
        
        treeQueue.add(root);
        
        while(!treeQueue.isEmpty())
        {
            TreeNode currenNode = treeQueue.getFirst(); //获取队首元素
            
            System.out.println(currenNode.val);//访问节点
            
            if(currenNode.left != null)
            {
                treeQueue.add(currenNode.left);//左子树进队列
            }
            
            if(currenNode.right != null)
            {
                treeQueue.add(currenNode.right);//右子树进队列
            }
            
            treeQueue.removeFirst();//队首元素访问完出队列
        }
    }
}