我在写一个函数“simplify”来简化多项式
simplify("2xy-yx")
可以返回
"xy"
,
simplify("-a+5ab+3a-c-2a")
可以返回
"-c+5ab"
等等。
我在合并相同单项式的阶段,但某些单项式的系数
+1
或
-1
. 我想把它们改成
+
或
-
. 但我不能直接删除1否则值为
+12
或
-18
将更改为
+2
和
-8
分别是。
例如
input = '3xy+y-2x+2xy'
到目前为止,我的过程告诉我:
Var = ['xy', 'y', 'x']
Coe = ['+5', '+1', '-2']
然后我得到了一个中间结果:
IR = ['+5xy', '+1y', '-2x']
我目前的解决方案:
[(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in IR ]
目前看来这项工作是为我做的,但看起来很笨重。我想知道是否有一个更干净和更简洁的方法来实现同样的目标。最好不用regex。
谢谢。
编辑:这个问题的代码。我还在调试呢。
def simplify(poly):
#If the first coefficient is positive, then I add a + for calculation later on
if poly[0] !='-':
poly = '+'+poly
L = list(poly)
#Put each monomial in a list as an element
Temp, e = [], ''
for i in L:
if i != '+' and i != '-':
e += i
else:
Temp.append(e)
e = ''
e += i
#The last one will be left out and the first one will be None
Temp.append(e)
Temp.pop(0)
#If the monomial only has a + or - in front of it, then give it a '1' so it's easier for calculation
SortAndGiveOne = [''.join(e[0] + '1' + e[1:]) if not e[1].isdigit() else e for e in Temp]
#Try to get letters from each element of the list
Var = [''.join(sorted(i for i in e if i.isalpha())) for e in SortAndGiveOne]
#Try to get coefficients from each element of the list
Coe = [''.join(i for i in e if not i.isalpha()) for e in SortAndGiveOne]
#Calculation of equivalent monomials
newvar = []
newcoe = []
for va, co in zip(Var, Coe):
try:
ind = newvar.index(va)
newcoe[ind] = str(int(newcoe[ind]) + int(co))
except ValueError:
newvar.append(va)
newcoe.append(co)
# Put the new lists together
Put_t = list(map(lambda x,y : y + x, newvar, newcoe))
# Add the plus sign as it will be gone if there was calculation involved.
FinalSign = ['+'+ e if e[0] != '+' and e[0] != '-' else e for e in Put_t]
#Delete the elements with 0 as coefficient
Delete0 = [e for e in FinalSign if not e[1]=='0']
#Change the +1 and -1 coefficients to + and -
Change1 = [(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in Delete0 ]
#Sort the list based on length and then lexi order
FS_sort = sorted(Change1, key = lambda s: (len(''.join(filter(str.isalpha, s))), (''.join(filter(str.isalpha, s)))))
#Join together as a list
JT = ''.join(FS_sort)
#Delete leading plus sign
if JT[0] == '+':
JT = JT[1:]
return JT