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

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/scratch/facebook/bst-checker.py

@@ -0,0 +1,49 @@
+from collections import deque
+
+class Node(object):
+    def __init__(self, value, left=None, right=None):
+        self.value = value
+        self.left = left
+        self.right = right
+
+    def is_bst(self):
+        s = []
+        s.append((float('-inf'), self, float('inf')))
+        while s:
+            lo, node, hi = s.pop()
+            if lo <= node.value <= hi:
+                node.left and s.append((lo, node.left, node.value))
+                node.right and s.append((node.value, node.right, hi))
+            else:
+                return False
+        return True
+
+
+x = Node(
+    50,
+    Node(
+        17,
+        Node(
+            12,
+            Node(9),
+            Node(14),
+        ),
+        Node(
+            23,
+            Node(19),
+        ),
+    ),
+    Node(
+        72,
+        Node(
+            54,
+            None,
+            Node(67)
+        ),
+        Node(76),
+    ),
+)
+
+
+assert x.is_bst()
+print("Success!")