solve: validate binary search tree

Author: sounmind

validate-binary-search-tree/evan.js

@@ -0,0 +1,28 @@
+/**
+ * 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 {boolean}
+ */
+function isValidBST(root, low = -Infinity, high = Infinity) {
+  if (root === null) {
+    return true;
+  }
+
+  if (root.val <= low || root.val >= high) {
+    return false;
+  }
+
+  return (
+    // left root should be less than current root
+    isValidBST(root.left, low, root.val) &&
+    // right root should be greater than current root
+    isValidBST(root.right, root.val, high)
+  );
+}