如何打印二叉树中每个节点的级别?

我不知道你在用什么语言,但这里是如何用JavaScript打印二叉树。

BinaryTree.prototype.preOrderTraversal = function(node){
    if(node !== null){
        console.log(node.data);
        this.preOrderTraversal(node.left);
        this.preOrderTraversal(node.right);
    }
};

/** 
 * Post traversal prototype function
 *          preforms recursive Postorder traversal on the tree
 *
 * @param  start node
 *
 * @return none
 * @throws none
 **/
BinaryTree.prototype.postOrderTraversal = function(node){
    if(node != null){
        this.postOrderTraversal(node.left);
        this.postOrderTraversal(node.right);
        console.log(node.data);
    }
};

/** 
 * Inorder traversal prototype function
 *          preforms recursive inorder traversal on the tree
 *
 * @param  start node
 *
 * @return none
 * @throws none
 **/
BinaryTree.prototype.inOrderTraversal = function(node){
    if(node != null){
        this.inOrderTraversal(node.left);
        console.log(node.data);
        this.inOrderTraversal(node.right);
    }
};

/** 
 * Depth Frist Search prototype function
 *          preforms Depth First Search on the tree
 *
 * @param  start node
 *
 * @return none
 * @throws none
 **/
BinaryTree.prototype.depthFirstSearch = function(node){
        if(node == null)
            return;

        var stack = [];
        stack.push(node);

        while (stack.length > 0) {
            console.log(node = stack.pop());
            if(node.right!=null) 
                stack.push(node.right);
            if(node.left!=null) 
                stack.push(node.left);          
        }
};

/** 
 * Breadth First Search prototype function
 *          preforms Breadth First Search on the tree
 *
 * @param  start node
 *
 * @return none
 * @throws none
 **/
BinaryTree.prototype.breadthFirstSearch = function(node){
    if(node == null)
        return;

    var queue = [];
    queue.push(node);

    while (queue.length > 0) {
        console.log((node = queue.shift()));
        if(node.left != null) 
            queue.push(node.left);          
        if(node.right != null) 
            queue.push(node.right);

    }
};

C#、Java、Visual basic中还有更多示例 here