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LeetCode/string-to-integer-atoi
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Implement atoi which converts a string to an integer. | |
The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value. | |
The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function. | |
If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed. | |
If no valid conversion could be performed, a zero value is returned. | |
Note: | |
Only the space character ' ' is considered as whitespace character. | |
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or INT_MIN (−231) is returned. | |
Example 1: | |
Input: "42" | |
Output: 42 | |
Example 2: | |
Input: " -42" | |
Output: -42 | |
Explanation: The first non-whitespace character is '-', which is the minus sign. | |
Then take as many numerical digits as possible, which gets 42. | |
Example 3: | |
Input: "4193 with words" | |
Output: 4193 | |
Explanation: Conversion stops at digit '3' as the next character is not a numerical digit. | |
Example 4: | |
Input: "words and 987" | |
Output: 0 | |
Explanation: The first non-whitespace character is 'w', which is not a numerical | |
digit or a +/- sign. Therefore no valid conversion could be performed. | |
Example 5: | |
Input: "-91283472332" | |
Output: -2147483648 | |
Explanation: The number "-91283472332" is out of the range of a 32-bit signed integer. | |
Thefore INT_MIN (−231) is returned. | |
My code: | |
class Solution: | |
def myAtoi(self, str): | |
""" | |
:type str: str | |
:rtype: int | |
""" | |
length=len(str) | |
tmp_list=[] | |
flag=False | |
start=0 | |
for i in range(length): | |
if str[i]==" " and i==start: | |
start+=1 | |
continue | |
if i==start and str[i]=='-': | |
flag=True | |
continue | |
if i==start and str[i]=='+': | |
flag=False | |
continue | |
if i==start and not (str[i].isdigit()) : | |
return 0 | |
if str[i].isdigit(): | |
tmp_list.append(int(str[i])) | |
else: | |
break | |
result=0 | |
for i in range(len(tmp_list)): | |
result=result*10+tmp_list[i] | |
if result>2**31-1 and not flag: | |
return 2**31-1 | |
if result>2**31 and flag: | |
return -2**31 | |
if flag: | |
return -result | |
return result | |
Solution: | |
https://leetcode.com/problems/string-to-integer-atoi/ |