二叉树的非递归遍历

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1. 递归实现

先序

public void preOrder(){
    preOrder(root);
}
private void preOrder(Node node){
    if(node != null){
        System.out.println(node.value);
        preOrder(node.left);
        preOrder(node.right);
    }
}

中序

public void midOrder(){
    midOrder(root);
}
private void midOrder(Node node){
    if(node != null){
        midOrder(node.left);
        System.out.println(node.value);
        midOrder(node.right);
    }
}

后序

public void postOrder(){
    postOrder(root);
}
private void postOrder(Node node){
    if(node != null){
        postOrder(node.left);
        postOrder(node.right);
        System.out.println(node.value);
    }
}

2. 非递归

前序

public void preOrderNew(){
    preOrderNew(root);
}
private void preOrderNew(Node node){
    if(node != null){
        LinkedList<Node> list = new LinkedList();
        list.addFirst(node);

        while(!list.isEmpty()){
            Node temp = (Node) list.removeFirst();
            if(temp.right != null){
                list.addFirst(temp.right);
            }
            if(temp.left != null){
                list.addFirst(temp.left);
            }
            System.out.println(temp.value);
        }
    }
}

中序

public void midOrderNew(){
    midOrderNew(root);
}
private void midOrderNew(Node node){
    LinkedList<Node> list = new LinkedList();
    while(!list.isEmpty() || node != null){
        if(node != null){
            list.addFirst(node);
            node = node.left;
        }else{
            node = list.removeFirst();
            System.out.println(node.value);
            node = node.right;
        }
    }
}

后序

public void postOrderNew(){
    postOrderNew(root);
}
private void postOrderNew(Node node){
    if(node != null){
        LinkedList<Node> list1 = new LinkedList();
        LinkedList<Node> list2 = new LinkedList();
        list1.addFirst(node);

        while(!list1.isEmpty()){
            Node temp = list1.removeFirst();
            list2.addFirst(temp);
            if(temp.left != null){
                list1.addFirst(temp.left);
            }
            if(temp.right != null){
                list1.addFirst(temp.right);
            }
        }
        while(!list2.isEmpty()){
            Node temp = list2.removeFirst();
            System.out.println(temp.value);
        }
    }
}