语法练习：front_back

语法练习：front_back

题目：front_back

Given a string, return a new string where the first and last chars have been exchanged.

front_back(‘code’) → ‘eodc’
front_back(‘a’) → ‘a’
front_back(‘ab’) → ‘ba’

我的解答：

def front_back(str):
  if len(str) == 0 or len(str) == 1:
    return str
  elif len(str) == 2:
    return (str[-1] + str[0])
  else:
    return str[-1] + str[1:-1] + str[0]
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Expected Run
front_back(‘code’) → ‘eodc’ ‘eodc’ OK
front_back(‘a’) → ‘a’ ‘a’ OK
front_back(‘ab’) → ‘ba’ ‘ba’ OK
front_back(‘abc’) → ‘cba’ ‘cba’ OK
front_back(‘’) → ‘’ ‘’ OK
front_back(‘Chocolate’) → ‘ehocolatC’ ‘ehocolatC’ OK
front_back(‘aavJ’) → ‘Java’ ‘Java’ OK
front_back(‘hello’) → ‘oellh’ ‘oellh’ OK

All Correct

标答：

def front_back(str):
  if len(str) <= 1:
    return str
  
  mid = str[1:len(str)-1]  # can be written as str[1:-1]
  
  # last + mid + first
  return str[len(str)-1] + mid + str[0]
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