JS 中的 DepthFirstInOrer - 测试代码无法打印值

Question

I've created a method to traverse Depth first in order with a recursion in my BinaryTree class.

I don't understand where to add this.value for the value of my left child and right child to be received in my test code as expected. I've tried every possible place but without success. when I use console.log to debug, i can only manage to get the value or [Function (anonymous)]

Method:

      traverseDepthFirstInOrder(fn) {

    //handle left child (if exists)
    if (this.left) {
      this.left.traverseDepthFirstInOrder(fn);
    }
    //handle right child (if exists)
    if (this.right) {
      this.right.traverseDepthFirstInOrder(fn);
    }
  }

testCode:

test("should call the fn on left nodes, center nodes, then right nodes", () => {
let test = [];
      binaryTree.add(4);
      binaryTree.add(14);
      binaryTree.add(6);
      binaryTree.add(16);
      binaryTree.add(2);
      binaryTree.add(12);
      binaryTree.traverseDepthFirstInOrder(e => test.push(e.value));
      expect(test).toEqual([2, 4, 6, 10, 12, 14, 16]);
    });

terminal failed:

• Expected - 9
  • Received + 1

Answer 1

This was what was meant in trincot's comment. This is supposed to traverse the tree in an inorder manner, calling the supplied function on every node. But you don't call the function. You're missing one line:

 class Tree { constructor (value, left = null, right = null) {this.value = value; this.left = left; this.right = right} traverseDepthFirstInOrder (fn) { //handle left child (if exists) if (this.left) { this.left.traverseDepthFirstInOrder(fn); } // handle the root node fn (this) // *** This line was missing *** //handle right child (if exists) if (this.right) { this.right.traverseDepthFirstInOrder(fn); } } } const binaryTree = new Tree (10, new Tree (4, new Tree (2), new Tree (6)), new Tree (14, new Tree (12), new Tree (16))) let test = []; binaryTree.traverseDepthFirstInOrder(e => test.push(e.value)); console.log (test)

Ignore the constructor and my method of creating the tree; I don't have the rest of the class you're using. But this change should fix your version as well.