二叉树非递归遍历（前序，中序，后续遍序）

 

public void preOrder(){  //非递归前序遍历
        System.out.print("前序遍历: ");
        SeqStack<BinaryNode> stack = new SeqStack<BinaryNode>();
        BinaryNode<E> p = this.root;

        while(p!=null||!stack.isEmpty()){
            if(p!=null){
                System.out.print(p+" ");
                stack.push(p);
                p=p.left;
            }else{
                p=stack.pop().right;
            }
        }
        System.out.println();
    }


    public void inOrder(){  //非递归中序遍历
        System.out.print("中序遍历： " );
        SeqStack<BinaryNode> stack = new SeqStack<BinaryNode>();
        BinaryNode<E> p = this.root;

        while(p!=null||!stack.isEmpty()){
            if(p!=null){
                stack.push(p);
                p=p.left;
            }else{
                p = stack.pop();
                System.out.print(p.data+" ");
                p=p.right;
            }
        }
        System.out.println();
    }

    public void postOrder(){   //非递归后续遍历
        System.out.print("后序遍历： " );
        SeqStack<BinaryNode> stack = new SeqStack<BinaryNode>();
        BinaryNode<E> p = this.root;
        BinaryNode<E> q =null;  //记录上一次的访问的结点

        while(p!=null||!stack.isEmpty()){
            while(p!=null){   //一直到最左下的结点
                stack.push(p);
                p=p.left;
            }
            p=stack.get();  //查看栈顶元素
            if(p.right==null||p.right==q){      //如果p没有右孩子或者其右孩子刚刚被访问过
                System.out.print(p.data+" ");
                stack.pop();
                q=p;
                p=null;
            }else {
                p=p.right;
            }

        }
    }


    public void levelOrder(){  //层次遍历 （思想：只读队列里的结点）
        SeqQueue<BinaryNode> queue = new SeqQueue<BinaryNode>();
        System.out.print("层次遍历： ");
        BinaryNode<E> p = this.root;

        while(p!=null||!queue.isEmpty()){
            System.out.print(p.data+" ");
            if(p.left!=null){
                queue.enqueue(p.left);
            }
            if(p.right!=null){
                queue.enqueue(p.right);
            }
            p=queue.dequeue();
        }
        System.out.println();
    }