Add ternary search and tests for it

Author: barmidrol

algorithms/searching/ternary_search.py

@@ -0,0 +1,22 @@
+"""
+    Ternary search
+    ---------------
+    Finds the maximum of unimodal function fn() within [left, right]
+    To find the minimum, revert the if/else statement or revert the comparison.
+
+    Time Complexity: O(log(n))
+
+"""
+
+
+def search(fn, left, right, precision):
+    while abs(right - left) > precision:
+        left_third = left + (right - left) / 3
+        right_third = right - (right - left) / 3
+
+        if fn(left_third) < fn(right_third):
+            left = left_third
+        else:
+            right = right_third
+
+    return (left + right) / 2

docs/searching.rst

@@ -25,3 +25,8 @@ Searching
     :members:
     :undoc-members:
     :show-inheritance:
+
+.. automodule:: algorithms.searching.ternary_search
+    :members:
+    :undoc-members:
+    :show-inheritance:

tests/test_searching.py

@@ -1,13 +1,15 @@
 """ Unit Tests for searching """
 import unittest
+import math
 
 from algorithms.searching import (
     binary_search,
     bmh_search,
     breadth_first_search,
     depth_first_search,
     kmp_search,
-    rabinkarp_search
+    rabinkarp_search,
+    ternary_search
 )
 
 
@@ -188,3 +190,18 @@ def test_rabinkarpsearch(self):
         rv2 = rabinkarp_search.search(self.string, "BCA")
         self.assertIs(rv1[0], 12)
         self.assertFalse(rv2)
+
+
+class TestTernarySearch(unittest.TestCase):
+    """
+    Tests teranry search algorithm on unimodal functions
+    """
+
+    def test_terarysearch(self):
+        self.function1 = lambda x: -(x - 2) ** 2
+        self.function2 = lambda x: math.cos(x)
+        self.eps = 1e-6
+        rv1 = ternary_search.search(self.function1, -2.0, 2.0, self.eps)
+        rv2 = ternary_search.search(self.function2, -2.0, 2.0, self.eps)
+        self.assertAlmostEqual(rv1, 2.0, 6)
+        self.assertAlmostEqual(rv2, 0.0, 6)