1. 把字符串转换成整数
写一个函数 StrToInt，实现把字符串转换成整数这个功能。不能使用 atoi 或者其他类似的库函数。
方法一：

def strToInt(s):res = 0max_value = 2**31 - 1min_value = -2**31i = 0sign = 1length = len(s)if not length:return reswhile i < length and s[i] == " ":i += 1if i == length:return resif s[i] == "-":sign = -1if s[i] in ["-", "+"]:i += 1for j in range(i, length):if s[j] < '0' or s[j] > '9':breakres = 10 * res + (ord(s[j]) - ord('0'))return max(min(res * sign, max_value), min_value)

方法二：

def strToInt(str):min_value = -(2 ** 31)max_value = 2 ** 31 - 1res = str.strip()match = Noneif res:match = re.match(r'^[+-]?\d+', res)if not match:return 0res = int(match.group())return min(max_value, max(min_value, res))