Applying Arithmetic Operations On List Of Numbers Without Repetition In Python
We've got the following python list: [1,2,3,10] I would like to accomplish the following: Create a function that takes in the list and figures out from the list of arithmetic opera
Solution 1:
I like sanyash's solution, but I think it can be done more elegantly, by using combinations of operands and than taking permutations, until the first with the right value is found:
from itertools import chain, permutations, combinations
def powerset(iterable):
xs = list(iterable)
return chain.from_iterable(combinations(xs, n) for n in range(len(xs) + 1))
def get_first_perm_with_value(operands, operators, expected_value):
if len(operands) == 0 or len(operands) == 0:
return []
all_operators = list(map(list, permutations(operators, len(operands) - 1)))
all_operands = list(map(list, permutations(operands, len(operands))))
for operator in all_operators:
for operand in all_operands:
result = [""] * (len(operand) + len(operator))
result[::2] = operand
result[1::2] = operator
eq = ''.join(result)
if int(eval(eq)) == expected_value:
return [(f'{eq}={expected_value}', operands)]
return []
lst_expr = []
for operands in map(list, powerset(['1', '2', '3', '10'])):
lst_expr += get_first_perm_with_value(operands, ['+','-','*','/'], 6)
print(lst_expr)
Returns:
[('2*3=6', ['2', '3']), ('2*3/1=6', ['1', '2', '3']), ('1+10/2=6', ['1', '2', '10']), ('2*10/3=6', ['2', '3', '10']), ('2*3+1/10=6', ['1', '2', '3', '10'])]
Solution 2:
Here is possible solution. We need to keep a sorted tuple of used numbers to avoid duplicates like 2*3 and 3*2.
from itertools import chain, permutations
defpowerset(iterable):
xs = list(iterable)
return chain.from_iterable(permutations(xs,n) for n inrange(len(xs)+1) )
lst_expr = []
for operands inmap(list, powerset(['1','2','3','10'])):
n = len(operands)
#print operandsif n > 1:
all_operators = map(list, permutations(['+','-','*','/'],n-1))
#print all_operators, operandsfor operators in all_operators:
exp = operands[0]
numbers = (operands[0],)
i = 1for operator in operators:
exp += operator + operands[i]
numbers += (operands[i],)
i += 1
lst_expr += [{'exp': exp, 'numbers': tuple(sorted(numbers))}]
lst_stages=[]
numbers_sets = set()
for item in lst_expr:
equation = item['exp']
numbers = item['numbers']
if numbers notin numbers_sets andeval(equation) == 6:
lst_stages.append(equation)
eq = str(equation) + '=' + str(eval(equation))
print(eq, numbers)
numbers_sets.add(numbers)
Output:
2*3=6 ('2', '3')
1+10/2=6.0 ('1', '10', '2')
2/1*3=6.0 ('1', '2', '3')
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