rearrange source files

* Add a useful `algorithms` package to provide convinient access to the
implemented algorithms.
* This allows to e.g. dynamically list available algorithms, which
greatly simplifies a lot of things.

7 files changed, 277 insertions, 0 deletions

diff --git a/algorithms/impl/__init__.py b/algorithms/impl/__init__.py
new file mode 100644
index 0000000..29cd51c
--- /dev/null
+++ b/algorithms/impl/__init__.py
@@ -0,0 +1,29 @@
+# Copyright 2016 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+_ALL_ALGORITHMS = {}
+
+def _refresh_algorithms():
+    _ALGORITHMS_NAME = '_ALGORITHMS'
+    global _ALL_ALGORITHMS
+    _ALL_ALGORITHMS = {}
+
+    from algorithms.algorithm import Algorithm
+
+    from importlib import import_module
+    import os.path
+    from pkgutil import iter_modules
+
+    for _, module_name, is_pkg in iter_modules([os.path.dirname(__file__)]):
+        if is_pkg:
+            continue
+        module = import_module('.' + module_name, __package__)
+        if hasattr(module, _ALGORITHMS_NAME):
+            module_algorithms = getattr(module, _ALGORITHMS_NAME)
+            for algorithm in module_algorithms:
+                assert isinstance(algorithm, Algorithm)
+                assert algorithm.get_codename() not in _ALL_ALGORITHMS
+                _ALL_ALGORITHMS[algorithm.get_codename()] = algorithm
+
+_refresh_algorithms()
diff --git a/algorithms/impl/bubble_sort.py b/algorithms/impl/bubble_sort.py
new file mode 100644
index 0000000..2abfc43
--- /dev/null
+++ b/algorithms/impl/bubble_sort.py
@@ -0,0 +1,39 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+def bubble_sort(xs):
+    while True:
+        swapped = False
+        for i in range(1, len(xs)):
+            if xs[i - 1] > xs[i]:
+                xs[i], xs[i - 1] = xs[i - 1], xs[i]
+                swapped = True
+        if not swapped:
+            break
+    return xs
+
+def bubble_sort_optimized(xs):
+    n  = len(xs)
+    while True:
+        new_n = 0
+        for i in range(1, n):
+            if xs[i - 1] > xs[i]:
+                xs[i], xs[i - 1] = xs[i - 1], xs[i]
+                new_n = i
+        n = new_n
+        if not n:
+            break
+    return xs
+
+if __name__ == '__main__':
+    import sys
+    xs = list(map(int, sys.argv[1:]))
+    print(bubble_sort(list(xs)))
+    print(bubble_sort_optimized(list(xs)))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('bubble_sort', 'Bubble sort', bubble_sort),
+        SortingAlgorithm('bubble_sort_optimized', 'Bubble sort (optimized)', bubble_sort_optimized),
+    ]
diff --git a/algorithms/impl/heapsort.py b/algorithms/impl/heapsort.py
new file mode 100644
index 0000000..db3b6bd
--- /dev/null
+++ b/algorithms/impl/heapsort.py
@@ -0,0 +1,59 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+# Disclaimer: implemented in the most literate way.
+
+def heapsort(xs):
+    _heapify(xs)
+    first, last = 0, len(xs) - 1
+    for end in range(last, first, -1):
+        xs[end], xs[first] = xs[first], xs[end]
+        _siftdown(xs, first, end - 1)
+    return xs
+
+# In a heap stored in a zero-based array,
+# left_child = node * 2 + 1
+# right_child = node * 2 + 2
+# parent = (node - 1) // 2
+
+def _get_parent(node):
+    return (node - 1) // 2
+
+def _get_left_child(node):
+    return node * 2 + 1
+
+def _get_right_child(node):
+    return node * 2 + 2
+
+def _heapify(xs):
+    last = len(xs) - 1
+    first_parent, last_parent = 0, _get_parent(last)
+    for parent in range(last_parent, first_parent - 1, -1):
+        _siftdown(xs, parent, last)
+
+def _siftdown(xs, start, end):
+    root = start
+    while True:
+        # We swap if there is at least one child
+        child = _get_left_child(root)
+        if child > end:
+            break
+        # If there are two children, select the minimum
+        right_child = _get_right_child(root)
+        if right_child <= end and xs[child] < xs[right_child]:
+            child = right_child
+        if xs[root] < xs[child]:
+            xs[root], xs[child] = xs[child], xs[root]
+            root = child
+        else:
+            break
+
+if __name__ == '__main__':
+    import sys
+    print(heapsort(list(map(int, sys.argv[1:]))))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('heapsort', 'Heapsort', heapsort),
+    ]
diff --git a/algorithms/impl/insertion_sort.py b/algorithms/impl/insertion_sort.py
new file mode 100644
index 0000000..f671712
--- /dev/null
+++ b/algorithms/impl/insertion_sort.py
@@ -0,0 +1,20 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+def insertion_sort(xs):
+    for i in range(1, len(xs)):
+        j = i
+        while j > 0 and xs[j - 1] > xs[j]:
+            xs[j], xs[j - 1] = xs[j - 1], xs[j]
+            j -= 1
+    return xs
+
+if __name__ == '__main__':
+    import sys
+    print(insertion_sort(list(map(int, sys.argv[1:]))))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('insertion_sort', 'Insertion sort', insertion_sort),
+    ]
diff --git a/algorithms/impl/merge_sort.py b/algorithms/impl/merge_sort.py
new file mode 100644
index 0000000..9fa96ec
--- /dev/null
+++ b/algorithms/impl/merge_sort.py
@@ -0,0 +1,34 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+def merge(left, right):
+    result = []
+    l, r = 0, 0
+    while l < len(left) and r < len(right):
+        if left[l] <= right[r]:
+            result.append(left[l])
+            l += 1
+        else:
+            result.append(right[r])
+            r += 1
+    if left:
+        result.extend(left[l:])
+    if right:
+        result.extend(right[r:])
+    return result
+
+def merge_sort(xs):
+    if len(xs) < 2:
+        return xs
+    mid = len(xs) // 2
+    return merge(merge_sort(xs[:mid]), merge_sort(xs[mid:]))
+
+if __name__ == '__main__':
+    import sys
+    print(merge_sort(list(map(int, sys.argv[1:]))))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('merge_sort', 'Merge sort', merge_sort),
+    ]
diff --git a/algorithms/impl/quicksort.py b/algorithms/impl/quicksort.py
new file mode 100644
index 0000000..32100b0
--- /dev/null
+++ b/algorithms/impl/quicksort.py
@@ -0,0 +1,74 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+from random import randrange
+
+def _partition(xs, beg, end, select_pivot):
+    pivot = select_pivot(xs, beg, end)
+    xs[pivot], xs[end] = xs[end], xs[pivot]
+    for i in range(beg, end):
+        if xs[i] <= xs[end]:
+            xs[i], xs[beg] = xs[beg], xs[i]
+            beg += 1
+    xs[beg], xs[end] = xs[end], xs[beg]
+    return beg
+
+def _quicksort(xs, beg, end, select_pivot):
+    if beg < end:
+        pivot = _partition(xs, beg, end, select_pivot)
+        _quicksort(xs, beg, pivot - 1, select_pivot)
+        _quicksort(xs, pivot + 1, end, select_pivot)
+
+def _select_first(xs, beg, end):
+    return beg
+
+def _select_second(xs, beg, end):
+    return beg + 1
+
+def _select_middle(xs, beg, end):
+    return (beg + end) // 2
+
+def _select_last(xs, beg, end):
+    return end
+
+def _select_random(xs, beg, end):
+    return randrange(beg, end + 1)
+
+def quicksort_first(xs):
+    _quicksort(xs, 0, len(xs) - 1, _select_first)
+    return xs
+
+def quicksort_second(xs):
+    _quicksort(xs, 0, len(xs) - 1, _select_second)
+    return xs
+
+def quicksort_middle(xs):
+    _quicksort(xs, 0, len(xs) - 1, _select_middle)
+    return xs
+
+def quicksort_last(xs):
+    _quicksort(xs, 0, len(xs) - 1, _select_last)
+    return xs
+
+def quicksort_random(xs):
+    _quicksort(xs, 0, len(xs) - 1, _select_random)
+    return xs
+
+if __name__ == '__main__':
+    import sys
+    xs = list(map(int, sys.argv[1:]))
+    print(quicksort_first(list(xs)))
+    print(quicksort_second(list(xs)))
+    print(quicksort_middle(list(xs)))
+    print(quicksort_last(list(xs)))
+    print(quicksort_random(list(xs)))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('quicksort_first', 'Quicksort (first element as pivot)', quicksort_first),
+        SortingAlgorithm('quicksort_second', 'Quicksort (second element as pivot)', quicksort_second),
+        SortingAlgorithm('quicksort_middle', 'Quicksort (middle element as pivot)', quicksort_middle),
+        SortingAlgorithm('quicksort_last', 'Quicksort (last element as pivot)', quicksort_last),
+        SortingAlgorithm('quicksort_random', 'Quicksort (random element as pivot)', quicksort_random),
+    ]
diff --git a/algorithms/impl/selection_sort.py b/algorithms/impl/selection_sort.py
new file mode 100644
index 0000000..d48c058
--- /dev/null
+++ b/algorithms/impl/selection_sort.py
@@ -0,0 +1,22 @@
+# Copyright 2015 Egor Tensin <Egor.Tensin@gmail.com>
+# This file is licensed under the terms of the MIT License.
+# See LICENSE.txt for details.
+
+def selection_sort(xs):
+    for i in range(len(xs) - 1):
+        min_i = i
+        for j in range(i + 1, len(xs)):
+            if xs[j] < xs[min_i]:
+                min_i = j
+        if min_i != i:
+            xs[i], xs[min_i] = xs[min_i], xs[i]
+    return xs
+
+if __name__ == '__main__':
+    import sys
+    print(selection_sort(list(map(int, sys.argv[1:]))))
+else:
+    from algorithms.algorithm import SortingAlgorithm
+    _ALGORITHMS = [
+        SortingAlgorithm('selection', 'Selection sort', selection_sort),
+    ]