Validate Binary Search Tree

Author: casentino

validate-binary-search-tree/casentino.ts

@@ -0,0 +1,39 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+class TreeNode {
+  val: number;
+  left: TreeNode | null;
+  right: TreeNode | null;
+  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+function isValidBST(root: TreeNode | null): boolean {
+  function recursiveSearch(node: TreeNode | null, min: number | null, max: number | null) {
+    if (!node) {
+      return true;
+    }
+    if (min !== null && node.val <= min) {
+      return false;
+    }
+    if (max !== null && node.val >= max) {
+      return false;
+    }
+    return recursiveSearch(node.left, min, node.val) && recursiveSearch(node.right, node.val, max);
+  }
+  return recursiveSearch(root, null, null);
+}