Python/strings/min_cost_string_conversion.py
2019-10-05 10:14:13 +05:00

119 lines
3.3 KiB
Python

"""
Algorithm for calculating the most cost-efficient sequence for converting one string into another.
The only allowed operations are
---Copy character with cost cC
---Replace character with cost cR
---Delete character with cost cD
---Insert character with cost cI
"""
def compute_transform_tables(X, Y, cC, cR, cD, cI):
X = list(X)
Y = list(Y)
m = len(X)
n = len(Y)
costs = [[0 for _ in range(n + 1)] for _ in range(m + 1)]
ops = [[0 for _ in range(n + 1)] for _ in range(m + 1)]
for i in range(1, m + 1):
costs[i][0] = i * cD
ops[i][0] = "D%c" % X[i - 1]
for i in range(1, n + 1):
costs[0][i] = i * cI
ops[0][i] = "I%c" % Y[i - 1]
for i in range(1, m + 1):
for j in range(1, n + 1):
if X[i - 1] == Y[j - 1]:
costs[i][j] = costs[i - 1][j - 1] + cC
ops[i][j] = "C%c" % X[i - 1]
else:
costs[i][j] = costs[i - 1][j - 1] + cR
ops[i][j] = "R%c" % X[i - 1] + str(Y[j - 1])
if costs[i - 1][j] + cD < costs[i][j]:
costs[i][j] = costs[i - 1][j] + cD
ops[i][j] = "D%c" % X[i - 1]
if costs[i][j - 1] + cI < costs[i][j]:
costs[i][j] = costs[i][j - 1] + cI
ops[i][j] = "I%c" % Y[j - 1]
return costs, ops
def assemble_transformation(ops, i, j):
if i == 0 and j == 0:
seq = []
return seq
else:
if ops[i][j][0] == "C" or ops[i][j][0] == "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])
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])))
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])
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])
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))