initial version of edit script.

editscript/edit_script.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python
+# encoding: utf-8
+
+import heapq # TODO: overkill. Bucketing is better
+from collections import defaultdict
+
+class GridPoint(object):
+    """Docstring for GridPoint """
+
+    __slots__ = ("parent", "cost",)
+
+    def __init__(self, parent, cost):
+        """@todo: to be defined
+
+        :parent: @todo
+        :cost: @todo
+        """
+        self._parent = parent
+        self._cost = cost
+
+def edit_script(a, b):
+
+    heap = [ (0,0,0,"") ]
+
+    while True:
+        cost, y, x,what = heapq.heappop(heap)
+
+        if x == len(a) and y == len(b):
+            return what
+
+        if x < len(a) and y < len(b) and a[x] == b[y]:
+            heapq.heappush(heap, (cost, y+1,x+1, what + "M"))
+        else:
+            if x < len(a) and y < len(b):
+                heapq.heappush(heap, (cost + 1, y+1, x+1, what + "S"))
+            if x < len(a):
+                heapq.heappush(heap, (cost + 1, y, x+1, what + "D"))
+            if y < len(b):
+                heapq.heappush(heap, (cost + 1, y+1, x, what + "I"))
+
+
+import unittest
+
+class TestEditScript(unittest.TestCase):
+    def test_empty_string(self):
+        rv = edit_script("","")
+        self.assertEqual(rv, "")
+
+    def test_all_match(self):
+        rv = edit_script("abcdef", "abcdef")
+        self.assertEqual("MMMMMM", rv)
+
+    def test_no_substr(self):
+        rv = edit_script("abc", "def")
+        self.assertEqual("SSS", rv)
+
+    def test_paper_example(self):
+        rv = edit_script("abcabba","cbabac")
+        self.assertEqual(rv, "SMDMMDMI")
+
+    def test_skiena_example(self):
+        rv = edit_script("thou shalt not", "you should not")
+        self.assertEqual(rv, "DSMMMMMISMSMMMM")
+if __name__ == '__main__':
+   unittest.main()
+   # k = TestEditScript()
+   # unittest.TextTestRunner().run(k)
+
+
+