2week: 98. Validate Binary Search Tree

Author: j2h30728

validate-binary-search-tree/j2h30728.ts

@@ -0,0 +1,22 @@
+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 valid(node, min, max) {
+    if (!node) return true;
+
+    if (node.val <= min || node.val >= max) return false;
+
+    return valid(node.left, min, node.val) && valid(node.right, node.val, max);
+  }
+
+  return valid(root, -Infinity, Infinity);
+}