二叉树的递归和迭代实现（java）

package 二叉树;
public class 递归 {    public class Node{        public int value;        public Node Left;        public Node Right;
        public Node(int data){            this.value = data;        }    }    public void preOrderRecur(Node head){        if(head == null){            return;        }        System.out.println(head.value+" ");        preOrderRecur(head.Left);        preOrderRecur(head.Right);    }    public void inOrederRecur(Node head){        if(head == null){            return;        }        inOrederRecur(head.Left);        System.out.println(head.value+" ");
        inOrederRecur(head.Right);    }    public void posOrederRecur(Node head){        if(head == null){            return;        }        posOrederRecur(head.Left);        posOrederRecur(head.Right);        System.out.println(head.value+" ");    }    }

package 二叉树;
import java.util.Stack;
public class 非递归 {    public class Node{        public int value;        public Node Left;        public Node Right;
        public Node(int data){            this.value = data;        }    }    //用自己的数据结构来模拟代替函数栈    public void preOrderUnRecur(Node head){        System.out.println("pre-order: ");        if(head != null){            Stack< Node> stack = new Stack<Node>();            stack.add(head);//插入根            while(!stack.empty()){                head = stack.pop();//弹出根                System.out.println(head.value+" ");                if(head.Right != null){                    stack.push(head.Right);//栈的先进后出，最后左边会先打印                }                if(head.Left != null){                    stack.push(head.Left);                }            }        }        System.out.println();    }
    //中 zuo,根，you    public void inOrderUnRecur(Node head){        System.out.println("in-order: ");        if(head != null){            Stack<Node> stack = new Stack<Node>();            while(!stack.empty() || head != null){                if(head!=null){                    stack.push(head);                    head = head.Left; //一直放左，直到碰到根      左根右                }else{                    head = stack.pop();                    System.out.println(head.value+" ");                    head = head.Right;                }            }        }        System.out.println();    }
    //后 zuo,you,根    public void posOrderUnRecur(Node head){        System.out.println("pos-order: ");        if(head != null){            Stack<Node> s1 = new Stack<Node>();//俩个栈实现            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.println(s2.pop()+" ");            }        }    }
}