1 files changed, 93 insertions, 0 deletions
diff --git a/users/wpcarro/scratch/facebook/hard/suffix-tree.py b/users/wpcarro/scratch/facebook/hard/suffix-tree.py
new file mode 100644
index 0000000000..782678fb82
--- /dev/null
+++ b/users/wpcarro/scratch/facebook/hard/suffix-tree.py
@@ -0,0 +1,93 @@
+import random
+from collections import deque
+
+def exists(pattern, tree):
+    """
+    Return true if `pattern` exists in `tree`.
+    """
+    if len(pattern) == 0:
+        return True
+    if len(pattern) == 1:
+        for branch in tree:
+            if branch[0] == pattern[0]:
+                return True
+        return False
+    for branch in tree:
+        if branch[0] == pattern[0]:
+            return exists(pattern[1:], branch[1])
+    return False
+
+# Branch :: (Char, [Branch])
+# SuffixTree :: [Branch]
+
+def suffix_tree(xs):
+    """
+    Create a suffix tree from the input string, `xs`.
+    """
+    root = []
+    for i in range(len(xs)):
+        curr = xs[i:]
+        parent = root
+        for c1 in curr:
+            grafted = False
+            for c2, children in parent:
+                if c1 == c2:
+                    grafted = True
+                    parent = children
+            if grafted:
+                continue
+            else:
+                children = []
+                child = (c1, children)
+                parent.append(child)
+                parent = children
+    return root
+
+def suffix_tree(x):
+    """
+    Creates a suffix from the input string, `x`. This implementation uses a
+    stack.
+    """
+    result = [None, []]
+    q = deque()
+    for i in range(len(x)):
+        q.append((result, x[i:]))
+    while q:
+        parent, x = q.popleft()
+        s = []
+        s.append((parent, x))
+        while s:
+            parent, x = s.pop()
+            if not x:
+                continue
+            c, rest = x[0], x[1:]
+            grafted = False
+            for child in parent[1]:
+                if c == child[0]:
+                    s.append((child, rest))
+                    grafted = True
+            if not grafted:
+                child = [c, []]
+                parent[1].append(child)
+                s.append((child, rest))
+    return result[1]
+
+################################################################################
+# Tests
+################################################################################
+
+x = random.choice(["burrito", "pizza", "guacamole"])
+tree = suffix_tree(x)
+for branch in tree:
+    print(branch)
+
+for _ in range(3):
+    n = len(x)
+    i, j = random.randint(0, n), random.randint(0, n)
+    pattern = x[min(i, j):max(i, j)]
+    print("Checking \"{}\" for \"{}\" ...".format(x, pattern))
+    print("Result: {}".format(exists(pattern, tree)))
+    pattern = random.choice(["foo", "bar", "baz"])
+    print("Checking \"{}\" for \"{}\" ...".format(x, pattern))
+    print("Result: {}".format(exists(pattern, tree)))
+    print()