add boilerplate for second edition

first_edition/ebook_src/abstract_structures/heap/find_N_largest_smallest_items_seq.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+import heapq
+
+def find_N_largest_items_seq(seq, N):
+    ''' find the N largest items in a sequence '''
+    return heapq.nlargest(N,seq)
+
+def find_N_smallest_items_seq(seq, N):
+    ''' find the N smallest items in a sequence '''
+    return heapq.nsmallest(N, seq)
+
+def find_smallest_items_seq_heap(seq):
+    ''' find the smallest items in a sequence using heapify first'''
+    ''' heap[0] is always the smallest item '''
+    ''' pops the smallest item, O(logN) '''
+    heapq.heapify(seq)
+    return heapq.heappop(seq)
+
+def find_smallest_items_seq(seq):
+    '''  if it is only one item, min() is faster '''
+    return min(seq)
+
+def find_N_smallest_items_seq_sorted(seq, N):
+    '''  N ~ len(seq), better sort instead'''
+    return sorted(seq)[:N]
+
+def find_N_largest_items_seq_sorted(seq, N):
+    '''  N ~ len(seq), better sort instead'''
+    return sorted(seq)[len(seq)-N:]
+
+
+def test_find_N_largest_smallest_items_seq(module_name='this module'):
+    seq = [1, 3, 2, 8, 6, 10, 9]
+    N = 3
+    assert(find_N_largest_items_seq(seq, N) == [10, 9, 8])
+    assert(find_N_largest_items_seq_sorted(seq, N) == [8, 9, 10])
+    assert(find_N_smallest_items_seq(seq, N) == [1,2,3])
+    assert(find_N_smallest_items_seq_sorted(seq, N) == [1,2,3])
+    assert(find_smallest_items_seq(seq) == 1)
+    assert(find_smallest_items_seq_heap(seq) == 1)
+
+    s = 'Tests in {name} have {con}!'
+    print(s.format(name=module_name, con='passed'))
+
+
+if __name__ == '__main__':
+    test_find_N_largest_smallest_items_seq()
+

first_edition/ebook_src/abstract_structures/heap/heapify.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+class Heapify(object):
+    def __init__(self, data=None):
+        self.data = data or []
+        for i in range(len(data)//2, -1, -1):
+            self.__max_heapify__(i)
+
+    def __repr__(self):
+        return '{}'.format(self.data)
+
+    def parent(self, i):
+        return i >> 1
+
+    def left_child(self, i):
+        return (i << 1) + 1
+
+    def right_child(self, i):
+        return (i << 1) + 2 # +2 instead of +1 because it's 0-indexed.
+
+    def __max_heapify__(self, i):
+        largest = i
+        left = self.left_child(i)
+        right = self.right_child(i)
+        n = len(self.data)
+        largest = (left < n and self.data[left] > self.data[i]) and left or i
+        largest = (right < n and self.data[right] > self.data[largest]) and right or largest
+        if i is not largest:
+            self.data[i], self.data[largest] = self.data[largest], self.data[i]
+            self.__max_heapify__(largest)
+
+    def extract_max(self):
+        n = len(self.data)
+        max_element = self.data[0]
+        self.data[0] = self.data[n - 1]
+        self.data = self.data[:n - 1]
+        self.__max_heapify__(0)
+        return max_element
+
+
+def test_Heapify():
+    l1 = [3, 2, 5, 1, 7, 8, 2]
+    h = Heapify(l1)
+    assert(h.extract_max() == 8)
+
+if __name__ == '__main__':
+    test_Heapify()

first_edition/ebook_src/abstract_structures/heap/merge_sorted_seqs.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+import heapq
+
+
+def merge_sorted_seq(seq1, seq2):
+    ''' merge two sorted sequences with little ovehead. the result
+        will be sorted, which is different of doing just +'''
+    result = []
+    for c in heapq.merge(seq1, seq2):
+        result.append(c)
+    return result
+
+
+def test_merge_sorted_seq(module_name='this module'):
+    seq1 = [1, 2, 3, 8, 9, 10]
+    seq2 = [2, 3, 4, 5, 6, 7, 9]
+    seq3 = seq1 + seq2
+    assert(merge_sorted_seqseq1, seq2) == sorted(seq3))
+
+
+
+if __name__ == '__main__':
+    test_merge_sorted_seq()
+

first_edition/ebook_src/abstract_structures/heap/priority_queue.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+import heapq
+
+class PriorityQueue(object):
+    ''' implements a priority queue class '''
+    def __init__(self):
+        self._queue = []
+        self._index = 0 # comparying same priority level
+
+    def push(self, item, priority):
+        heapq.heappush(self._queue, (-priority, self._index, item))
+        self._index += 1
+
+    def pop(self):
+        return heapq.heappop(self._queue)[-1]
+
+
+class Item:
+    def __init__(self, name):
+        self.name = name
+    def __repr__(self):
+        return "Item({!r})".format(self.name)
+
+
+def test_PriorityQueue():
+    ''' push and pop are all O(logN) '''
+    q = PriorityQueue()
+    q.push(Item('test1'), 1)
+    q.push(Item('test2'), 4)
+    q.push(Item('test3'), 3)
+    assert(str(q.pop()) == "Item('test2')")
+
+
+if __name__ == '__main__':
+    test_PriorityQueue()
+
+