Validate Binary Search Tree

Author: TonyKim9401

validate-binary-search-tree/TonyKim9401.java

@@ -0,0 +1,17 @@
+// TC: O(n)
+// visit all nodes to compare
+// SC: O(n)
+// recursion requires O(n) SC in the worst case
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return dfs(root, Long.MIN_VALUE, Long.MAX_VALUE);
+    }
+
+    private boolean dfs(TreeNode node, long min, long max) {
+        if (node == null) return true;
+
+        if (node.val <= min || node.val >= max) return false;
+        return dfs(node.left, min, node.val) &&
+                dfs(node.right, node.val, max);
+    }
+}