二叉树的非递归遍历&递归遍历

package 实际问题;import java.util.Stack;public class MyTree{    public static void main(String[] s){        new MyTree();    }    public MyTree(){        TreeNode root = init();//初始化二叉树并返回根节点        System.out.println("递归先序遍历");        preorder(root);        System.out.println();        System.out.println("递归中序遍历");        inorder(root);        System.out.println();        System.out.println("递归后续遍历");        posorder(root);        System.out.println();        System.out.println("非递归先序遍历");        _preorder(root);        System.out.println();        System.out.println("非递归中序遍历");        _inorder(root);        System.out.println();        System.out.println("非递归后续遍历");        _posorder(root);        System.out.println();    }        public void preorder(TreeNode root){//递归二叉树的前序遍历        if(root != null){            System.out.print(root.getValue());//访问节点值            preorder(root.getLeft());            preorder(root.getRight());        }    }    public void _preorder(TreeNode root){             //非递归二叉树的前序遍历        Stack<TreeNode> stack = new Stack<TreeNode>();//定义堆栈存储        while(!(root == null && stack.isEmpty())){            while (root != null) {                  System.out.print(root.getValue());                  stack.push(root);                  root = root.getLeft();            }              if (!stack.isEmpty()) {                  root = stack.pop();                  root = root.getRight();              }          }              }    public void inorder(TreeNode root){//递归中序遍历        if(root != null){            inorder(root.getLeft());            System.out.print(root.getValue());            inorder(root.getRight());        }    }    public void _inorder(TreeNode root){//非递归中序遍历        Stack<TreeNode> stack = new Stack<TreeNode>();        while(!(root == null && stack.isEmpty())){            while(root != null){//先找到最深的左子树                stack.push(root);                root = root.getLeft();            }            //找到最深左子树后开始访问            root = stack.pop();            System.out.print(root.getValue());            //开始寻找右子树            root = root.getRight();        }    }    public void posorder(TreeNode root){//递归后序遍历        if(root != null){            posorder(root.getLeft());            posorder(root.getRight());            System.out.print(root.getValue());        }    }    //非递归的后续遍历需要两次访问节点，最后一次访问节点为准    private int sign = 0;//得当当前访问节点的次数    public void _posorder(TreeNode root){        Stack stack = new Stack();//定义一个可以存放TreeNode 和 Integer的栈        while(!(root == null && stack.isEmpty())){            if(root != null){//找最深左子树                stack.push(root);//将当前节点压入堆栈                stack.push(1);//并标记当前访问节点的次数                root = root.getLeft();            }else{//找到最深左子树后                while(!stack.isEmpty()){                    sign = (Integer)stack.pop();//出栈标记                    root = (TreeNode)stack.pop();//出栈节点                    if(sign == 1){//地一次访问节点                        stack.push(root);                        stack.push(2);                        root = root.getRight();//将节点指向右子树并开始访问指向右子树的左子树                        break;                    }else if(sign == 2){//当第二次出栈时访问节点                        System.out.print(root.getValue());                        root = null;                    }                }            }        }    }    public TreeNode init(){//二叉树的初始化        TreeNode d = new TreeNode('4');        TreeNode e = new TreeNode('5');        TreeNode f = new TreeNode('6');        TreeNode g = new TreeNode('7');        TreeNode b = new TreeNode('2',d,e);        TreeNode c = new TreeNode('3',f,g);        TreeNode a = new TreeNode('1',b,c);        return a;    }}//建立二叉树的节点类class TreeNode{    public char data;    public TreeNode left,right;    public TreeNode(char data){        this(data,null,null);    }    public TreeNode(char data,TreeNode left,TreeNode right){        this.data = data;        this.left = left;        this.right = right;    }    public TreeNode getLeft(){//返回左子树        return left;    }    public TreeNode getRight(){//返回右子树        return right;    }    public char getValue(){//访问节点值        return data;    }}