Add 'universe/' from commit '8ad51b24dd'

git-subtree-dir: universe
git-subtree-mainline: 15110e6de9
git-subtree-split: 8ad51b24dd

universe/data_structures_and_algorithms/kth-to-last.py

@@ -0,0 +1,82 @@
+import unittest
+
+
+################################################################################
+# Solution
+################################################################################
+def length(x):
+    if not x:
+        return 0
+    else:
+        count = 1
+        while x:
+            x = x.next
+            count += 1
+        return count
+
+
+def kth_to_last_node(k, x):
+    hops = length(x) - 1
+    dest = hops - k
+
+    if k == 0:
+        raise Exception("Our God doesn't support this kind of behavior.")
+
+    if dest < 0:
+        raise Exception('Value k to high for list.')
+
+    while dest > 0:
+        x = x.next
+        dest -= 1
+
+    return x
+
+
+################################################################################
+# Tests
+################################################################################
+class Test(unittest.TestCase):
+    class LinkedListNode(object):
+        def __init__(self, value, next=None):
+            self.value = value
+            self.next = next
+
+        def get_values(self):
+            node = self
+            values = []
+            while node is not None:
+                values.append(node.value)
+                node = node.next
+            return values
+
+    def setUp(self):
+        self.fourth = Test.LinkedListNode(4)
+        self.third = Test.LinkedListNode(3, self.fourth)
+        self.second = Test.LinkedListNode(2, self.third)
+        self.first = Test.LinkedListNode(1, self.second)
+
+    def test_first_to_last_node(self):
+        actual = kth_to_last_node(1, self.first)
+        expected = self.fourth
+        self.assertEqual(actual, expected)
+
+    def test_second_to_last_node(self):
+        actual = kth_to_last_node(2, self.first)
+        expected = self.third
+        self.assertEqual(actual, expected)
+
+    def test_first_node(self):
+        actual = kth_to_last_node(4, self.first)
+        expected = self.first
+        self.assertEqual(actual, expected)
+
+    def test_k_greater_than_linked_list_length(self):
+        with self.assertRaises(Exception):
+            kth_to_last_node(5, self.first)
+
+    def test_k_is_zero(self):
+        with self.assertRaises(Exception):
+            kth_to_last_node(0, self.first)
+
+
+unittest.main(verbosity=2)