add: validateBST solution

Author: Cyjin-jani

validate-binary-search-tree/Cyjin-jani.js

@@ -0,0 +1,23 @@
+const isValidBST = function (root) {
+  let answer = true;
+
+  function validateRecursion(node, min, max) {
+    if (!node) return;
+
+    if (node.val >= max || node.val <= min) {
+      answer = false;
+      return;
+    }
+    if (node.val <= min || node.val >= max) {
+      answer = false;
+      return;
+    }
+
+    validateRecursion(node.left, min, node.val);
+    validateRecursion(node.right, node.val, max);
+  }
+
+  validateRecursion(root, -Infinity, Infinity);
+
+  return answer;
+};