validateBST.js

/*
Given a node of a binary search tree, validate the binary search tree.
  - Ensure that every node's left hand child is less than the parent node's value
  - Ensure that every node's right hand child is greater than the parent
*/

function validate(node, min = null, max = null) {
  if (max !== null && node.data > max) {
    return false;
  }
  
  if (min !== null && node.data < min) {
    return false;
  }
  
  if (node.left && !validate(node.left, min, node.data)) {
    return false;
  }
  
  if (node.right && !validate(node.right, node.data, max)) {
    return false;
  }
  
  return true;
}