题目
Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.
The algorithm for myAtoi(string s) is as follows:
- Whitespace: Ignore any leading whitespace (“ “).
- Signedness: Determine the sign by checking if the next character is ‘-‘ or ‘+’, assuming positivity if neither present.
- Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.
- Rounding: If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then round the integer to remain in the range. Specifically, integers less than -231 should be rounded to -231, and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result.
解题思路
先判断正负，之后遍历数字，如果超过范围则返回最大/小值
代码
class Solution:
def myAtoi(self, s: str) -> int:
s = s.strip()
if len(s) == 0:
return 0
INT_MAX = 2147483647
INT_MIN = -2147483648
flag = 1
if s[0] == '-':
flag = -1
s = s[1:]
elif s[0] == '+':
s = s[1:]
res = 0
for c in s:
if not c.isdigit():
break
res *= 10
res += ord(c) - ord('0')
if flag == 1:
if res > 2147483647:
return INT_MAX
else:
if res > 2147483648:
return INT_MIN
return res * flag
