算法-二叉树遍历（递归和非递归）

import java.util.ArrayList;import java.util.LinkedList;import java.util.List;import java.util.Queue;import java.util.Scanner;import java.util.Stack;/** * Created by mifeng on 8/8/17. */class Node {    public String data;    public Node left;    public Node right;}class BiTree {    Node root;    public BiTree(){        this.root = null;    }}public class TreeApp {    /**     * 先序递归建立二叉树     * @param node     * @return     */    public static Node create(Node node){        Scanner in = new Scanner(System.in);        String value = in.next();        if("#".equals(value) ){            node = null;        }else{            node = new Node();            node.data = value;            node.left = create(node.left);            node.right = create(node.right);        }        return node;    }    /**     * 先序遍历二叉树-递归形式     * @param root     */    public static void preOrderVisitByRecursive(Node root){        if(root == null){            return;        }else{            System.out.print(root.data);            preOrderVisitByRecursive(root.left);            preOrderVisitByRecursive(root.right);        }    }    //先序遍历二叉树-非递归    public static void preOrderVisit(Node root){        if(root == null){            return;        }else{//            Stack<String> stack = new Stack<String>();//            stack.push(root.data);//            System.out.println(stack.pop());            Stack<Node> stack = new Stack<Node>();            stack.push(root);//            System.out.println(stack.pop());            while (stack.size()!=0){//                Node currentNode = root;//                //stack.push(currentNode.data);//                if(root.right!=null)//                    stack.push(root.right.data);//                if(root.left!=null)//                    stack.push(root.left.data);//                System.out.println(stack.pop());//                //root = root.right;                Node currentNode = stack.pop();                System.out.print(currentNode.data);                //stack.push(currentNode.data);//                if(root.right!=null)//                    stack.push(root.right);//                if(root.left!=null)//                    stack.push(root.left);//                System.out.println(stack.pop());                if(currentNode.right!=null)                    stack.push(currentNode.right);                if(currentNode.left!=null)                    stack.push(currentNode.left);                //System.out.println(stack.pop());            }//            while(stack.size()!=0){//                stack.pop();//            }//            Stack<Node> stack = new Stack<Node>();//            stack.push(root);        }    }    public static void preOrderVisit2(Node root){        Stack<String> stack = new Stack<String>();        if(root == null){            return;        }else{            stack.push(root.data);            while(true){                System.out.println(root.data);                if(root.right!=null)                    stack.push(root.right.data);                if(root.left!=null)                    stack.push(root.left.data);                String data = stack.pop();                System.out.println(data);            }        }    }    //中序遍历-递归    public static void InOrderVisitByRecursive(Node root){        if(root == null){            return;        }        InOrderVisitByRecursive(root.left);        System.out.print(root.data);        InOrderVisitByRecursive(root.right);    }    //中序遍历-非递归    public static void InOrderVisit(Node root){        Stack<String> stack = new Stack<String>();        if(root!=null){            stack.push(root.data);            while(root!=null){                root = root.left;            }        }    }    public static void InorderVisit2(Node root){        Stack<Node> stack = new Stack<Node>();        if(root!=null){            stack.push(root);            while(root!=null){                stack.push(root);                root = root.left;            }            Node currentNode = stack.pop();            System.out.print(currentNode.data);            root = currentNode.right;            System.out.println(currentNode.data);        }    }    public static void InOrderVisit3(Node root){         Stack<Node> stack = new Stack<Node>();         if(root!=null){             //stack.push(root);             while(!stack.isEmpty()||root!=null){                 if(root!=null){                     stack.push(root);                     root = root.left;                 }else{                     Node currentNode = stack.pop();                     System.out.print(currentNode.data);                     root = currentNode.right;                 }             }//             Node currentNode = stack.pop();//             System.out.print(currentNode.data);//             root = currentNode.right;//             System.out.println(currentNode.data);        }    }    //层次序列化二叉树    public static void visitByLevel(Node head){        Queue<Node> queue = new LinkedList<Node>();        if(head == null){            return ;        }        queue.offer(head);        while(!queue.isEmpty()){            Node currNode = queue.poll();            System.out.println(currNode.data);            if(currNode.left!=null)                queue.offer(currNode.left);            if(currNode.right!=null)                queue.offer(currNode.right);        }        //return "";    }    public static void main(String[] args){        BiTree tree = new BiTree();        tree.root = create(tree.root);        //System.out.println(tree.root.data);        //System.out.println(tree.root.left.data);        System.out.println("先序遍历二叉树-递归");        preOrderVisitByRecursive(tree.root);        System.out.println("先序遍历二叉树-非递归");        preOrderVisit(tree.root);        System.out.println("中序遍历二叉树-递归");        InOrderVisitByRecursive(tree.root);        System.out.println("中序遍历二叉树-非递归");        InOrderVisit3(tree.root);        System.out.println("层次遍历：");        visitByLevel(tree.root);        //List<String> list = new ArrayList<String>(new ArrayList<String>());    }}