Implement and test longest consecutive sequence algorithm for binary …

…trees

tree/binary_tree/longest_consecutive_sequence/longest_consecutive_sequence.py

@@ -1,6 +1,3 @@
-maxlen = 0
-
-
 class Node:
     def __init__(self, val=None):
         self.left = None
@@ -15,21 +12,22 @@ def longest_consecutive(root):
     """
     if not root:
         return 0
-    DFS(root, 0, root.val)
-    return maxlen
+    return DFS(root, None, 0)
 
 
-def DFS(root, cur, target):
-    global maxlen
+def DFS(root, parent, length):
     if not root:
-        return
-    if root.val == target:
-        cur += 1
+        return length
+
+    if parent and root.val == parent.val + 1:
+        length += 1
     else:
-        cur = 1
-    maxlen = max(cur, maxlen)
-    DFS(root.left, cur, root.val + 1)
-    DFS(root.right, cur, root.val + 1)
+        length = 1
+
+    left_length = DFS(root.left, root, length)
+    right_length = DFS(root.right, root, length)
+
+    return max(length, left_length, right_length)
 
 
 if __name__ == '__main__':

tree/binary_tree/longest_consecutive_sequence/test_longest_consecutive_sequence.py

@@ -0,0 +1,36 @@
+import unittest
+from longest_consecutive_sequence import Node, longest_consecutive
+
+class TestLongestConsecutiveSequence(unittest.TestCase):
+    def test_example_case(self):
+        root = Node(1)
+        root.right = Node(3)
+        root.right.left = Node(2)
+        root.right.right = Node(4)
+        root.right.right.right = Node(5)
+        self.assertEqual(longest_consecutive(root), 3)
+
+    def test_empty_tree(self):
+        self.assertEqual(longest_consecutive(None), 0)
+
+    def test_single_node(self):
+        root = Node(1)
+        self.assertEqual(longest_consecutive(root), 1)
+
+    def test_no_consecutive_sequence(self):
+        root = Node(1)
+        root.left = Node(3)
+        root.right = Node(5)
+        self.assertEqual(longest_consecutive(root), 1)
+
+    def test_multiple_consecutive_sequences(self):
+        root = Node(1)
+        root.left = Node(2)
+        root.left.left = Node(3)
+        root.right = Node(4)
+        root.right.right = Node(5)
+        root.right.right.right = Node(6)
+        self.assertEqual(longest_consecutive(root), 3)
+
+if __name__ == '__main__':
+    unittest.main()