• 15 is maximum

Question related to mission Pearls in the Box

 

I'm sorry for the format, it's hard to paste.

import re
def checkio(marbles, step):
b=marbles.count("b")
n=len(marbles)    
for i in range(1,step+1):
    if i==1:
        c="(b-0)" 
    else:
        pat='b'+(i-1)*'.\w'
        s=re.findall(pat,c)
        for i in s:                
            ti='('+i+')'+'*('+i+'-1)'+'+(n-('+i+'))*('+i+'+1)'
            c=c.replace(i,ti)
            #print(c)
d=1-eval(c)/(n**step) 
d=round(d,2)
print(d)
return d
if __name__ == '__main__':
assert checkio("wwwwwwwwwwwwwwwwwwww",14) == 0.64, "1st example"

I want to use "re" to get formula in stringļ¼Œ then use "eval" to get the result, but when the step bigger than 14, that will cost too much time... Is there any way to simplify it?

Created at: Feb. 23, 2018, 3:40 a.m.; Updated at: Feb. 23, 2018, 3:49 a.m.