Java 非递归实现 二叉树的前中后遍历以及层级遍历

class MyBinaryTree<T> {
    BinaryNode<T> root;

    public MyBinaryTree() {
        root = new BinaryNode<>();
    }

    /**
     * 堆栈进行先序遍历
     *
     * @param ts
     */
    public void preorderTraversal(T... ts) {
        Stack<BinaryNode<T>> binaryStack = new Stack<>();
        BinaryNode<T> temp = root;
        while (!binaryStack.isEmpty() || temp != null) {
            if (temp != null) {
                // 处理
                System.out.println(temp.data);
                // 先序
                if (temp != null) {
                    binaryStack.push(temp);
                }
                temp = temp.left;
            } else {
                temp = binaryStack.pop();
                temp = temp.right != null ? temp.right : null;
            }
        }
    }

    /**
     * 堆栈中序遍历
     *
     * @param ts
     */
    public void inorderTraversal(T... ts) {
        Stack<BinaryNode<T>> binaryStack = new Stack<>();
        BinaryNode<T> temp = root;
        while (!binaryStack.isEmpty() || temp != null) {
            if (temp != null) {
                binaryStack.push(temp);
                temp = temp.left;
            } else {
                temp = binaryStack.pop();
                // 处理
                System.out.println(temp.data);
                temp = temp.right != null ? temp.right : null;
            }
        }
    }

    /**
     * 堆栈后序遍历
     *
     * @param ts
     */
    public void postorderTraversal(T... ts) {
        Stack<BinaryNode<T>> binaryStack = new Stack<>();
        BinaryNode<T> temp = root;
        BinaryNode<T> node = null;
        while (!binaryStack.isEmpty() || temp != null) {
            if (temp != null) {
                binaryStack.push(temp);
                temp = temp.left;
            } else {
                temp = binaryStack.pop();
                if (temp.right == null || temp.right == node) {
                    // 处理
                    System.out.println(temp.data);
                    node = temp;
                    temp = null;
                } else {
                    binaryStack.push(temp);
                    temp = temp.right;
                    binaryStack.push(temp);
                    temp = temp.left;
                }
            }
        }
    }

    /**
     * 层级遍历
     */
    public void levelTraversal() {
        BinaryNode<T> temp = root;
        Queue<BinaryNode<T>> queue = new LinkedList<>();
        queue.add(temp);
        while(!queue.isEmpty()) {
            temp = queue.poll();
　　　　　　　// 处理
            System.out.println(temp.data);
            if(temp.left!=null) {
                queue.add(temp.left);
            }
            if(temp.right!=null) {
                queue.add(temp.right);
            }
        }
    }
}

class BinaryNode<T> {
    BinaryNode<T> left;
    T data;
    BinaryNode<T> right;

    public BinaryNode() {
    }

    public BinaryNode(BinaryNode<T> left, T data, BinaryNode<T> right) {
        this.left = left;
        this.data = data;
        this.right = right;
    }
}    

测试代码：

    private MyBinaryTree<String> binaryTree;

    @Before
    public void setUp() {
        binaryTree = new MyBinaryTree<>();
        binaryTree.root.data = "A";
        binaryTree.root.left = new BinaryNode<>(new BinaryNode<>(null, "D", null), "B", null);
        binaryTree.root.right = new BinaryNode<>(new BinaryNode<>(null, "F", null), "C",
                new BinaryNode<>(null, "E", null));
    }

    @Test
    public void preorderTest() {
        binaryTree.preorderTraversal();
        System.out.println("---------------先序遍历------------------");
    }

    @Test
    public void inorderTest() {
        binaryTree.inorderTraversal();
        System.out.println("---------------中序遍历------------------");
    }

    @Test
    public void postorderTest() {
        binaryTree.postorderTraversal();
        System.out.println("---------------后序遍历------------------");
    }

    @Test
    public void levelTest() {
        binaryTree.levelTraversal();
        System.out.println("---------------层级遍历------------------");
    }