Validate Binary Search Tree / 중급

Author: oh-chaeyeon

oh-chaeyeon/5주차_트리/Validate_Binary_Search_Tree.js

@@ -0,0 +1,24 @@
+/**
+ * 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}
+ */
+var isValidBST = function (root) {
+  function validate(node, lower, upper) {
+    if (!node) return true;
+
+    const val = node.val;
+    if (val <= lower || val >= upper) return false;
+
+    return validate(node.left, lower, val) && validate(node.right, val, upper);
+  }
+
+  return validate(root, -Infinity, Infinity);
+};