adding merge sort

Author: oppianmatt

.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>PythonPractice</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.python.pydev.PyDevBuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.python.pydev.pythonNature</nature>
+	</natures>
+</projectDescription>

.pydevproject

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+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<?eclipse-pydev version="1.0"?>
+
+<pydev_project>
+<pydev_pathproperty name="org.python.pydev.PROJECT_SOURCE_PATH">
+<path>/PythonPractice/src</path>
+</pydev_pathproperty>
+<pydev_property name="org.python.pydev.PYTHON_PROJECT_VERSION">python 2.7</pydev_property>
+<pydev_property name="org.python.pydev.PYTHON_PROJECT_INTERPRETER">Default</pydev_property>
+</pydev_project>

src/sorting/__init__.py

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+'''
+Created on May 8, 2012
+
+@author: matt
+
+Example merge sort
+'''
+from random import Random
+
+    
+def merge_sort(left, right=None):
+    
+    if right == None:
+        mid = len(left) / 2
+        return merge_sort(left[:mid], left[mid:])
+    
+    # handle no length
+    if not left: return right
+    if not right: return left
+    
+    # handle lengths of 1
+    if len(left) == len(right) == 1:
+        if left[0] > right[0]:
+            # swap
+            return [right[0], left[0]]
+        # left and right sorted in order and length of 1 each so return as new array
+        return [left[0], right[0]]
+        
+    # split left and right and sort those
+    mid = (len(left) / 2) or 1
+    left = merge_sort(left[:mid], left[mid:])
+        
+    # split right and sort those
+    mid = (len(right) / 2) or 1
+    right = merge_sort(right[:mid], right[mid:])
+    
+    # merge
+    A = []
+    for i in xrange(len(left) + len(right)):
+        l = None
+        r = None
+        
+        if len(left):
+            l = left[0]
+        else:
+            # no more left so append all of right
+            A.extend(right)
+            return A
+        
+        if len(right):
+            r = right[0]
+        else:
+            # no more right
+            A.extend(left)
+            return A
+            
+        # if left is smaller then put it next, otherwise r
+        if l <= r:
+            A.append(l)
+            del left[0]
+        else:
+            A.append(r)
+            del right[0]
+    return A
+        
+
+import unittest
+
+
+class Test(unittest.TestCase):
+
+
+    def testSimple(self):
+        self.assertEqual([1, 2, 3], merge_sort([3, 2, 1]))
+        self.assertEqual([1, 2, 3], merge_sort([1, 3, 2]))
+        
+        self.assertEqual([1, 3, 4, 4, 5, 5, 7, 8], merge_sort([4, 5, 1, 7, 8, 4, 3, 5]))
+        
+    def testRandom10(self):
+        random = Random()
+        pop = range(10) + range(10)
+        A = random.sample(pop, 10)
+        self.assertEquals(sorted(A), merge_sort(A))
+        
+    def testRandom32767(self):
+        random = Random()
+        max = 32767
+        pop = range(max) + range(max)
+        A = random.sample(pop, max)
+        self.assertEquals(sorted(A), merge_sort(A))
+
+
+if __name__ == "__main__":
+    #import sys;sys.argv = ['', 'Test.testSimple']
+    unittest.main()