8. String to Integer (atoi)
String, AMateList ·Problem Statement
link: LeetCode.cn LeetCode 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 is 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.
Example:
Input: s = "42"
Output: 42
Input: ` s = “ -042”
**Output:** -42`
Solution Approach
Algorithm
Implement
class Solution:
def myAtoi(self, s: str) -> int:
#s.lstrip()
#check - +
# isdigit
# check min_int max_int
s = s.lstrip()
isNegative = 1
n = len(s)
res = 0
i = 0
if n <= 0:
return 0
if s[i] == "-":
isNegative = -1
i += 1
elif s[i] == "+":
i += 1
while i < n and s[i] == 0:
i += 1
while i < n:
if s[i].isdigit():
res = res * 10 + int(s[i])
i += 1
else:
break
res = res * isNegative
if res < - 2**31:
res = -2**31
if res > 2**31 - 1:
res = 2**31 - 1
return res