如何在python中优化for循环？

Question

I was trying to roll the character string in python Example : s='abz' roll=[3,2,1]

1. roll[0]=abz become bca
2. roll[1]= bca becomes cda
3. roll[2]= cda becomes dda I want to return dda

for i in roll:           
     s = ''.join([letters[(letters.index(c)+1)%len(letters)] for c in s[:i]]) + s[i:]
    
 return s

few test cases are failing on hackerrank due to time constraints, could someone please help me in optimizing this code.

Answer 1

I think you want ord() , which is the inverse of chr() ; once your char is a number, it's easier to +1 (don't forget to wrap)

then use a method to process each string (call this fn in a loop - once per word):

def increment(in_str):
  # loop over each letter
  for idx in range(0,len(in_str)):
    # convert to a number
    char_val = ord(in_str[idx])
    if char_val == ord("z"):
      # if 'z' - replace with 'a'
      in_str[idx] = chr("a")
    else:
      # otherwise +1 and convert back to char
      in_str[idx] = chr(char_val + 1)