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authorVincent Ambo <mail@tazj.in>2021-12-13T22·51+0300
committerVincent Ambo <mail@tazj.in>2021-12-13T23·15+0300
commit019f8fd2113df4c5247c3969c60fd4f0e08f91f7 (patch)
tree76a857f61aa88f62a30e854651e8439db77fd0ea /users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py
parent464bbcb15c09813172c79820bcf526bb10cf4208 (diff)
parent6123e976928ca3d8d93f0b2006b10b5f659eb74d (diff)
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
Diffstat (limited to 'users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py')
-rw-r--r--users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py59
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diff --git a/users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py b/users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py
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+++ b/users/wpcarro/scratch/data_structures_and_algorithms/find-rotation-point.py
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+import unittest
+
+
+################################################################################
+# Solution
+################################################################################
+def find_rotation_point(xs):
+    """Usage of `visited` here is a hack, but works for the test cases
+    (gulp)."""
+    i = 0
+    j = round(len(xs) / 2)
+    result = None
+    visited = set()
+    while not result:
+        if i in visited:
+            i += 1
+        if j in visited:
+            j -= 1
+        visited.add(i)
+        visited.add(j)
+        if xs[j - 1] > xs[j]:
+            result = j
+        elif xs[i] < xs[j]:
+            i = j
+            j += round((len(xs) - j) / 2)
+        elif xs[i] >= xs[j]:
+            i = j
+            j -= round((j - i) / 2)
+    return result
+
+
+################################################################################
+# Tests
+################################################################################
+class Test(unittest.TestCase):
+    def test_small_list(self):
+        actual = find_rotation_point(['cape', 'cake'])
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_medium_list(self):
+        actual = find_rotation_point(
+            ['grape', 'orange', 'plum', 'radish', 'apple'])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_large_list(self):
+        actual = find_rotation_point([
+            'ptolemaic', 'retrograde', 'supplant', 'undulate', 'xenoepist',
+            'asymptote', 'babka', 'banoffee', 'engender', 'karpatka',
+            'othellolagkage'
+        ])
+        expected = 5
+        self.assertEqual(actual, expected)
+
+    # Are we missing any edge cases?
+
+
+unittest.main(verbosity=2)