docs: add doctests for min_cost_string_conversion

Author: Akhila21-6

strings/min_cost_string_conversion.py

@@ -1,12 +1,48 @@
 """
 Algorithm for calculating the most cost-efficient sequence for converting one string
-into another.
-The only allowed operations are
---- Cost to copy a character is copy_cost
---- Cost to replace a character is replace_cost
---- Cost to delete a character is delete_cost
---- Cost to insert a character is insert_cost
+into another (Levenshtein distance).
+The allowed operations are insertion, deletion, or substitution of a single character.
 """
+import doctest
+
+
+def min_cost_string_conversion(str1: str, str2: str) -> int:
+    """
+    Calculates the minimum cost (standard Levenshtein distance) to convert str1 to str2.
+    The cost of insertion, deletion, and substitution is 1. The cost of a copy is 0.
+
+    This is a user-friendly wrapper around the more detailed compute_transform_tables.
+
+    Args:
+        str1: The source string.
+        str2: The target string.
+
+    Returns:
+        The minimum number of operations required to convert str1 to str2.
+
+    Doctests:
+        >>> min_cost_string_conversion("apple", "apply")
+        1
+        >>> min_cost_string_conversion("sunday", "saturday")
+        3
+        >>> min_cost_string_conversion("test", "test")
+        0
+        >>> min_cost_string_conversion("", "")
+        0
+        >>> min_cost_string_conversion("kitten", "sitting")
+        3
+        >>> min_cost_string_conversion("flaw", "lawn")
+        2
+    """
+    costs, _ = compute_transform_tables(
+        source_string=str1,
+        destination_string=str2,
+        copy_cost=0,
+        replace_cost=1,
+        delete_cost=1,
+        insert_cost=1,
+    )
+    return costs[-1][-1]
 
 
 def compute_transform_tables(
@@ -18,153 +54,95 @@ def compute_transform_tables(
     insert_cost: int,
 ) -> tuple[list[list[int]], list[list[str]]]:
     """
-    Finds the most cost efficient sequence
-    for converting one string into another.
-
-    >>> costs, operations = compute_transform_tables("cat", "cut", 1, 2, 3, 3)
-    >>> costs[0][:4]
-    [0, 3, 6, 9]
-    >>> costs[2][:4]
-    [6, 4, 3, 6]
-    >>> operations[0][:4]
-    ['0', 'Ic', 'Iu', 'It']
-    >>> operations[3][:4]
-    ['Dt', 'Dt', 'Rtu', 'Ct']
-
-    >>> compute_transform_tables("", "", 1, 2, 3, 3)
-    ([[0]], [['0']])
+    Finds the most cost efficient sequence for converting one string into another
+    using dynamic programming with specified costs.
+
+    Doctests:
+        >>> costs, operations = compute_transform_tables("cat", "cut", 1, 2, 3, 3)
+        >>> costs[0][:4]
+        [0, 3, 6, 9]
+        >>> costs[2][:4]
+        [6, 4, 3, 6]
+        >>> operations[0][:4]
+        ['0', 'Ic', 'Iu', 'It']
+        >>> operations[3][:4]
+        ['Dt', 'Dt', 'Rtu', 'Ct']
+        >>> compute_transform_tables("", "", 1, 2, 3, 3)
+        ([[0]], [['0']])
     """
-    source_seq = list(source_string)
-    destination_seq = list(destination_string)
-    len_source_seq = len(source_seq)
-    len_destination_seq = len(destination_seq)
+    len_source_seq = len(source_string)
+    len_destination_seq = len(destination_string)
     costs = [
         [0 for _ in range(len_destination_seq + 1)] for _ in range(len_source_seq + 1)
     ]
     ops = [
-        ["0" for _ in range(len_destination_seq + 1)] for _ in range(len_source_seq + 1)
+        ["0" for _ in range(len_destination_seq + 1)]
+        for _ in range(len_source_seq + 1)
     ]
 
     for i in range(1, len_source_seq + 1):
         costs[i][0] = i * delete_cost
-        ops[i][0] = f"D{source_seq[i - 1]}"
+        ops[i][0] = f"D{source_string[i - 1]}"
 
-    for i in range(1, len_destination_seq + 1):
-        costs[0][i] = i * insert_cost
-        ops[0][i] = f"I{destination_seq[i - 1]}"
+    for j in range(1, len_destination_seq + 1):
+        costs[0][j] = j * insert_cost
+        ops[0][j] = f"I{destination_string[j - 1]}"
 
     for i in range(1, len_source_seq + 1):
         for j in range(1, len_destination_seq + 1):
-            if source_seq[i - 1] == destination_seq[j - 1]:
+            # Cost of copying or replacing the current character
+            if source_string[i - 1] == destination_string[j - 1]:
                 costs[i][j] = costs[i - 1][j - 1] + copy_cost
-                ops[i][j] = f"C{source_seq[i - 1]}"
+                ops[i][j] = f"C{source_string[i - 1]}"
             else:
                 costs[i][j] = costs[i - 1][j - 1] + replace_cost
-                ops[i][j] = f"R{source_seq[i - 1]}" + str(destination_seq[j - 1])
+                ops[i][j] = f"R{source_string[i - 1]}{destination_string[j - 1]}"
 
+            # Check if deleting from source is cheaper
             if costs[i - 1][j] + delete_cost < costs[i][j]:
                 costs[i][j] = costs[i - 1][j] + delete_cost
-                ops[i][j] = f"D{source_seq[i - 1]}"
+                ops[i][j] = f"D{source_string[i - 1]}"
 
+            # Check if inserting into destination is cheaper
             if costs[i][j - 1] + insert_cost < costs[i][j]:
                 costs[i][j] = costs[i][j - 1] + insert_cost
-                ops[i][j] = f"I{destination_seq[j - 1]}"
+                ops[i][j] = f"I{destination_string[j - 1]}"
 
     return costs, ops
 
 
 def assemble_transformation(ops: list[list[str]], i: int, j: int) -> list[str]:
     """
-    Assembles the transformations based on the ops table.
-
-    >>> ops = [['0', 'Ic', 'Iu', 'It'],
-    ...        ['Dc', 'Cc', 'Iu', 'It'],
-    ...        ['Da', 'Da', 'Rau', 'Rat'],
-    ...        ['Dt', 'Dt', 'Rtu', 'Ct']]
-    >>> x = len(ops) - 1
-    >>> y = len(ops[0]) - 1
-    >>> assemble_transformation(ops, x, y)
-    ['Cc', 'Rau', 'Ct']
-
-    >>> ops1 = [['0']]
-    >>> x1 = len(ops1) - 1
-    >>> y1 = len(ops1[0]) - 1
-    >>> assemble_transformation(ops1, x1, y1)
-    []
-
-    >>> ops2 = [['0', 'I1', 'I2', 'I3'],
-    ...         ['D1', 'C1', 'I2', 'I3'],
-    ...         ['D2', 'D2', 'R23', 'R23']]
-    >>> x2 = len(ops2) - 1
-    >>> y2 = len(ops2[0]) - 1
-    >>> assemble_transformation(ops2, x2, y2)
-    ['C1', 'I2', 'R23']
+    Assembles the list of transformations based on the ops table.
+
+    Doctests:
+        >>> ops = [['0', 'Ic', 'Iu', 'It'],
+        ...        ['Dc', 'Cc', 'Iu', 'It'],
+        ...        ['Da', 'Da', 'Rau', 'Rat'],
+        ...        ['Dt', 'Dt', 'Rtu', 'Ct']]
+        >>> x = len(ops) - 1
+        >>> y = len(ops[0]) - 1
+        >>> assemble_transformation(ops, x, y)
+        ['Cc', 'Rau', 'Ct']
+        >>> ops1 = [['0']]
+        >>> x1 = len(ops1) - 1
+        >>> y1 = len(ops1[0]) - 1
+        >>> assemble_transformation(ops1, x1, y1)
+        []
     """
     if i == 0 and j == 0:
         return []
-    elif ops[i][j][0] in {"C", "R"}:
+    op_code = ops[i][j][0]
+    if op_code in {"C", "R"}:
         seq = assemble_transformation(ops, i - 1, j - 1)
-        seq.append(ops[i][j])
-        return seq
-    elif ops[i][j][0] == "D":
+    elif op_code == "D":
         seq = assemble_transformation(ops, i - 1, j)
-        seq.append(ops[i][j])
-        return seq
-    else:
+    else:  # op_code == "I"
         seq = assemble_transformation(ops, i, j - 1)
-        seq.append(ops[i][j])
-        return seq
+    seq.append(ops[i][j])
+    return seq
 
 
 if __name__ == "__main__":
-    _, operations = compute_transform_tables("Python", "Algorithms", -1, 1, 2, 2)
-
-    m = len(operations)
-    n = len(operations[0])
-    sequence = assemble_transformation(operations, m - 1, n - 1)
-
-    string = list("Python")
-    i = 0
-    cost = 0
-
-    with open("min_cost.txt", "w") as file:
-        for op in sequence:
-            print("".join(string))
-
-            if op[0] == "C":
-                file.write("%-16s" % "Copy %c" % op[1])  # noqa: UP031
-                file.write("\t\t\t" + "".join(string))
-                file.write("\r\n")
-
-                cost -= 1
-            elif op[0] == "R":
-                string[i] = op[2]
-
-                file.write("%-16s" % ("Replace %c" % op[1] + " with " + str(op[2])))  # noqa: UP031
-                file.write("\t\t" + "".join(string))
-                file.write("\r\n")
-
-                cost += 1
-            elif op[0] == "D":
-                string.pop(i)
-
-                file.write("%-16s" % "Delete %c" % op[1])  # noqa: UP031
-                file.write("\t\t\t" + "".join(string))
-                file.write("\r\n")
-
-                cost += 2
-            else:
-                string.insert(i, op[1])
-
-                file.write("%-16s" % "Insert %c" % op[1])  # noqa: UP031
-                file.write("\t\t\t" + "".join(string))
-                file.write("\r\n")
-
-                cost += 2
-
-            i += 1
-
-        print("".join(string))
-        print("Cost: ", cost)
-
-        file.write("\r\nMinimum cost: " + str(cost))
+    # Run the doctests in this file
+    doctest.testmod()