Binary Tree Level Order Traversal

https://leetcode.com/problems/binary-tree-level-order-traversal/

class TreeNode {
  constructor(val) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

function traverse(root) {
  const result = [];
  if (root === null) {
    return result;
  }

  const queue = [];
  queue.push(root);

  while (queue.length > 0) {
    const levelSize = queue.length;
    const currentLevel = [];

    for (let i = 0; i < levelSize; i++) {
      const currentNode = queue.shift();

      currentLevel.push(currentNode.val);

      if (currentNode.left !== null) {
        queue.push(currentNode.left);
      }
      if (currentNode.right !== null) {
        queue.push(currentNode.right);
      }
    }

    result.push(currentLevel);
  }

  return result;
}

const root = new TreeNode(12);
root.left = new TreeNode(7);
root.right = new TreeNode(1);
root.left.left = new TreeNode(9);
root.right.left = new TreeNode(10);
root.right.right = new TreeNode(5);

console.log(`Level order traversal: ${JSON.stringify(traverse(root))}`);

Time Complexity O(n)/Space Complexity O(n)

https://medium.com/swlh/binary-tree-level-order-traversal-a12df61a85d0