cleaning up and organizing old problems (builtin)

src/searching_and_sorting/binary_search.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+
+def binary_search_rec(array, item, lo=0, hi = None):
+    '''
+    >>> binary_search_rec([2,3,5,6,8,10,15,23], 15)
+    (True, 6)
+    >>> binary_search_rec([2,3,5,6,8,10,15,23], 4)
+    False
+    '''
+    hi = hi or len(array)
+    if hi < lo :
+        return False
+
+    mid = (hi + lo)//2
+
+    if array[mid] == item:
+        return True, mid
+    elif array[mid] < item:
+        return binary_search_rec(array, item, mid + 1, hi)
+    else:
+        return binary_search_rec(array[:mid], item, lo, mid -1)
+
+
+
+def binary_search_iter(array, item):
+    '''
+    >>> binary_search_iter([2,3,5,6,8,10,15,23], 15)
+    (True, 6)
+    >>> binary_search_iter([2,3,5,6,8,10,15,23], 4)
+    False
+    '''
+    hi = len(array)
+    lo = 0
+
+    while lo < hi:
+        mid = (hi+lo)//2
+        if array[mid] == item:
+            return True, mid
+        elif array[mid] > item:
+            hi = mid
+        else:
+            lo  = mid + 1
+    return False
+
+
+
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+

src/searching_and_sorting/merge_and_sort_two_arrays.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+'''
+You have two arrays with N integers in them. Merge those arrays using a
+recursive algorithm so that the integers in the final array are sorted.
+'''
+
+def merge_arrays(a1, a2):
+    '''
+    >>> merge_arrays([5, 4, 3], [6, 2, 9])
+    [2, 3, 4, 5, 6, 9]
+    >>> merge_arrays([2, 6], [6, 2])
+    [2, 2, 6, 6]
+    >>> merge_arrays([], [])
+    []
+    '''
+    # if they are not sorted yet
+    a1.sort()
+    a2.sort()
+
+    merge = []
+    p1, p2 = 0, 0
+
+    while p1 < len(a1) and p2 < len(a2):
+        if a1[p1] <= a2[p2]:
+            merge.append(a1[p1])
+            p1 += 1
+        else:
+            merge.append(a2[p2])
+            p2 +=1
+
+    if a1[p1:]:
+        merge.extend(a1[p1:])
+
+    if a2[p2:]:
+        merge.extend(a2[p2:])
+
+    return merge
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+

src/searching_and_sorting/quick_sort.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+def qs(array):
+    '''
+    >>> qs([4,1,6,2,7,9,3])
+    [1, 2, 3, 4, 6, 7, 9]
+    '''
+    if len(array) < 2:
+        return array
+
+    piv = len(array)//2
+    piv_element = array[piv]
+    new_array = array[:piv] + array[piv+1:]
+
+    left  = [a for a in new_array if a <= piv_element]
+    right = [a for a in new_array if a > piv_element]
+
+
+    return qs(left) + [array[piv]] + qs(right)
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()