Improve min_cost_string_conversion with validation, case-insensitive option, and more tests

strings/min_cost_string_conversion.py

@@ -1,170 +1,44 @@
-"""
-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
-"""
-
-
 def compute_transform_tables(
-    source_string: str,
-    destination_string: str,
-    copy_cost: int,
-    replace_cost: int,
-    delete_cost: int,
-    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']])
-    """
-    source_seq = list(source_string)
-    destination_seq = list(destination_string)
-    len_source_seq = len(source_seq)
-    len_destination_seq = len(destination_seq)
-    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)
-    ]
-
-    for i in range(1, len_source_seq + 1):
-        costs[i][0] = i * delete_cost
-        ops[i][0] = f"D{source_seq[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 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]:
-                costs[i][j] = costs[i - 1][j - 1] + copy_cost
-                ops[i][j] = f"C{source_seq[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])
-
-            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]}"
-
-            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]}"
-
-    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']
-    """
-    if i == 0 and j == 0:
-        return []
-    elif ops[i][j][0] in {"C", "R"}:
-        seq = assemble_transformation(ops, i - 1, j - 1)
-        seq.append(ops[i][j])
-        return seq
-    elif ops[i][j][0] == "D":
-        seq = assemble_transformation(ops, i - 1, j)
-        seq.append(ops[i][j])
-        return seq
-    else:
-        seq = assemble_transformation(ops, i, j - 1)
-        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
+    s1, s2, insert_cost, delete_cost, replace_cost, swap_cost, ignore_case=False
+):
+    if ignore_case:
+        s1, s2 = s1.lower(), s2.lower()
+
+    m, n = len(s1), len(s2)
+
+    # cost table
+    dp = [[0] * (n + 1) for _ in range(m + 1)]
+    # operation table
+    op = [["0"] * (n + 1) for _ in range(m + 1)]
+
+    # Initialize base cases
+    for i in range(1, m + 1):
+        dp[i][0] = i * delete_cost
+        op[i][0] = "D" + s1[i - 1]
+    for j in range(1, n + 1):
+        dp[0][j] = j * insert_cost
+        op[0][j] = "I" + s2[j - 1]
+
+    # Fill DP tables
+    for i in range(1, m + 1):
+        for j in range(1, n + 1):
+            if s1[i - 1] == s2[j - 1]:
+                dp[i][j] = dp[i - 1][j - 1]
+                op[i][j] = "C" + s1[i - 1]
             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))
+                replace = dp[i - 1][j - 1] + replace_cost
+                insert = dp[i][j - 1] + insert_cost
+                delete = dp[i - 1][j] + delete_cost
+
+                # Choose min cost, tie-breaking in order: replace > insert > delete
+                min_cost = min(replace, insert, delete)
+                dp[i][j] = min_cost
+
+                if min_cost == replace:
+                    op[i][j] = "R" + s2[j - 1]
+                elif min_cost == insert:
+                    op[i][j] = "I" + s2[j - 1]
+                else:
+                    op[i][j] = "D" + s1[i - 1]
+
+    return dp, op