mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-24 05:21:09 +00:00
115 lines
2.6 KiB
Python
115 lines
2.6 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))
|