Good afternoon! Here's our prompt for today.

Can you write a function to traverse a binary tree in-order, and print out the value of each node as it passes?

1  4
2   \
3    5
4   /
5  6

The example would output [4, 6, 5] since there is no left child for 4, and 6 is visited in-order before 5.

The definition of a tree node is as follows:

1function Node(val) {
2  this.val = val;
3  this.left = null;
4  this.right = null;
5}

Follow up: you'll likely get the recursive solution first, could you do it iteratively?

Constraints

• Number of vertices in the tree <= 100000
• The values of the vertices in the tree will be between -1000000000 and 1000000000
• Expected time complexity : O(n)
• Expected space complexity : O(1)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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  assertIsFunction(inorderTraversal, '`inorderTraversal` should be a function');

var assert = require('assert');

​

function inorderTraversal(root) {

  return root;

}

​

function Node(val) {

  this.val = val;

  this.left = null;

  this.right = null;

}

​

// Regular binary trees

var tree1 = new Node(4);

tree1.left = new Node(1);

tree1.right = new Node(3);

​

var tree2 = new Node(5);

tree2.left = new Node(10);

tree2.left.left = new Node(17);

tree2.left.right = new Node(3);

tree2.right = new Node(8);

​

// Binary search trees

var tree3 = new Node(6);

tree3.left = new Node(3);

​

var tree4 = new Node(5);

tree4.left = new Node(3);

Here's a video of us explaining the solution.

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Here's how we would solve this problem...

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