二叉树遍历

非递归

import java.util.Stack;
public class PreOrderUnRecur {
    public static class Node{
        public int value;
        public Node left;
        public Node right;
        public Node(int data){
            this.value = data;
        }
    }
    public static void preOrder(Node head){
        if(head != null){
            Stack<Node> stack = new Stack<Node>();
            stack.push(head);
            while(!stack.isEmpty()){
                head = stack.pop();
                System.out.print(head.value + " ");
                if(head.right != null){
                    stack.push(head.right);
                }
                if(head.left != null){
                    stack.push(head.left);
                }
            }
        }
    }
    public static void inOrder(Node head){
        if(head != null){
            Stack<Node> stack = new Stack<Node>();
            while(head != null || !stack.isEmpty() ){
                if(head != null){
                    stack.push(head);
                    head = head.left;
                }else{
                    head = stack.pop();
                    System.out.print(head.value + " ");
                    head = head.right;
                }
            }
        }
    }
    public static void posOrder(Node head){
        if(head != null){
            Stack<Node> s1 = new Stack<Node>();
            Stack<Node> s2 = new Stack<Node>();
            s1.push(head);
            while(!s1.isEmpty()){
                head = s1.pop();
                s2.push(head);
                if(head.left != null){
                    s1.push(head.left);
                }
                if(head.right != null){
                    s1.push(head.right);
                }
            }
            while(!s2.isEmpty()){
                System.out.print(s2.pop().value + " ");
            }
        }
    }
    public static void main(String[] args) {
        Node head = new Node(5);
        head.left = new Node(3);
        head.right = new Node(8);
        head.left.left = new Node(2);
        head.left.right = new Node(4);
        head.left.left.left = new Node(1);
        head.right.left = new Node(7);
        head.right.left.left = new Node(6);
        head.right.right = new Node(10);
        head.right.right.left = new Node(9);
        head.right.right.right = new Node(11);


        System.out.print("pre-order: ");
        preOrder(head);
        System.out.println();
        System.out.print("in-order: ");
        inOrder(head);
        System.out.println();
        System.out.print("pos-order: ");
        posOrder(head);
    }
}