1
var isUnivalTree = function (root) {
2
  if (!root) {
3
    return false;
4
  }
5

6
  const prev = root.val;
7
  const nodes = [root];
8

9
  for (const node of nodes) {
10
    if (node.val !== prev) {
11
      return false;
12
    }
13

14
    if (node.left) {
15
      nodes.push(node.left);
16
    }
17

18
    if (node.right) {
19
      nodes.push(node.right);
20
    }
21
  }
22

23
  return true;
24
};