// https://www.freecodecamp.org/learn/coding-interview-prep/data-structures/check-if-tree-is-binary-search-tree

var displayTree = (tree) => console.log(JSON.stringify(tree, null, 2));
function Node(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}
function BinarySearchTree() {
  this.root = null;
}
function isBinarySearchTree(tree) {
  // Only change code below this line
  if (tree.root === null) return true;
  const stack = [tree.root];
  while (stack.length) {
    const node = stack.pop();
    const leftChild = node.left;
    if (leftChild !== null) {
      stack.push(leftChild);
      if (node.value <= leftChild.value) return false;
    }
    const rightChild = node.right;
    if (rightChild !== null) {
      stack.push(rightChild);
      if (node.value > rightChild.value) return false;
    }
  }
  return true;
  // Only change code above this line
}