Merge pull request neetcode-gh#643 from diss1993/ticket/98

Swift | 98. Validate Binary Search Tree

Author: Ahmad-A0

swift/98-Validate-Binary-Search-Tree.swift

@@ -0,0 +1,13 @@
+class Solution {
+  func isValidBST(_ root: TreeNode?) -> Bool {
+      return isBst(root, min: Int.min, max: Int.max)
+  }
+
+  private func isBst(_ node: TreeNode?, min: Int, max: Int) -> Bool {
+    if node == nil { return true }
+    if node!.val <= min || node!.val >= max { return false }
+      let lc = isBst(node?.left, min: min, max: node!.val)
+      let rc = isBst(node?.right, min: node!.val, max: max)
+    return lc && rc
+  }
+}