add mdbn question

Author: betomoedano

binary-trees/maximum-difference-between-node-and-ancestor.js

@@ -0,0 +1,31 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+
+// Time O(n) where n is the number of nodes
+// Space O(n)
+var maxAncestorDiff = function (root) {
+  if (root === null) return;
+  return helper(root, root.val, root.val);
+};
+
+function helper(node, currMax, currMin) {
+  if (node === null) {
+    return currMax - currMin;
+  } else {
+    currMax = Math.max(currMax, node.val);
+    currMin = Math.min(currMin, node.val);
+    const left = helper(node.left, currMax, currMin);
+    const right = helper(node.right, currMax, currMin);
+    return Math.max(left, right);
+  }
+}