subtree(users/wpcarro): docking briefcase at '24f5a642' r/3226

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c09813172c79820bcf526bb10cf4208
git-subtree-split: 24f5a642af3aa1627bbff977f0a101907a02c69f
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

1 files changed, 14 insertions, 0 deletions

diff --git a/users/wpcarro/scratch/facebook/interview-cake/bst-checker.py b/users/wpcarro/scratch/facebook/interview-cake/bst-checker.py
new file mode 100644
index 0000000000..bbd52fa9c6
--- /dev/null
+++ b/users/wpcarro/scratch/facebook/interview-cake/bst-checker.py
@@ -0,0 +1,14 @@
+def is_valid(node):
+    """
+    Return True if `node` is a valid binary search tree.
+    """
+    s = []
+    s.append((float('-inf'), node, float('inf')))
+    while s:
+        lo, node, hi = s.pop()
+        if lo <= node.value <= hi:
+            node.lhs and s.append((lo, node.lhs, node.value))
+            node.rhs and s.append((node.value, node.rhs, hi))
+        else:
+            return False
+    return True