動機
打從心底不想重寫這題
Problem
Implement the myAtoi(string s)
function, which converts a string to a 32-bit signed integer (similar to C/C++'s atoi
function).
The algorithm for myAtoi(string s)
is as follows:
- Read in and ignore any leading whitespace.
- Check if the next character (if not already at the end of the string) is
'-'
or'+'
. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present. - Read in next the characters until the next non-digit charcter or the end of the input is reached. The rest of the string is ignored.
- Convert these digits into an integer (i.e.
123 -> 123
,0032 -> 32
). If no digits were read, then the integer is0
. Change the sign as necessary (from step 2). - If the integer is out of the 32-bit signed integer range
[-231, 231 - 1]
, then clamp the integer so that it remains in the range. Specifically, integers less than-231
should be clamped to-231
, and integers greater than231 - 1
should be clamped to231 - 1
. - Return the integer as the final result.
Note:
- Only the space character
' '
is considered a whitespace character. - Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.
Example 1:
Input: s = 42Output: 42Explanation: The underlined characters are what is read in, the caret is the current reader position.Step 1: 42 (no characters read because there is no leading whitespace) ^Step 2: 42 (no characters read because there is neither a '-' nor '+') ^Step 3: 42 (42 is read in) ^The parsed integer is 42.Since 42 is in the range [-231, 231 - 1], the final result is 42.
Example 2:
Input: s = -42Output: -42Explanation:Step 1: -42 (leading whitespace is read and ignored) ^Step 2: -42 ('-' is read, so the result should be negative) ^Step 3: -42 (42 is read in) ^The parsed integer is -42.Since -42 is in the range [-231, 231 - 1], the final result is -42.
Example 3:
Input: s = 4193 with wordsOutput: 4193Explanation:Step 1: 4193 with words (no characters read because there is no leading whitespace) ^Step 2: 4193 with words (no characters read because there is neither a '-' nor '+') ^Step 3: 4193 with words (4193 is read in; reading stops because the next character is a non-digit) ^The parsed integer is 4193.Since 4193 is in the range [-231, 231 - 1], the final result is 4193.
Example 4:
Input: s = words and 987Output: 0Explanation:Step 1: words and 987 (no characters read because there is no leading whitespace) ^Step 2: words and 987 (no characters read because there is neither a '-' nor '+') ^Step 3: words and 987 (reading stops immediately because there is a non-digit 'w') ^The parsed integer is 0 because no digits were read.Since 0 is in the range [-231, 231 - 1], the final result is 0.
Example 5:
Input: s = -91283472332Output: -2147483648Explanation:Step 1: -91283472332 (no characters read because there is no leading whitespace) ^Step 2: -91283472332 ('-' is read, so the result should be negative) ^Step 3: -91283472332 (91283472332 is read in) ^The parsed integer is -91283472332.Since -91283472332 is less than the lower bound of the range [-231, 231 - 1], the final result is clamped to -231 = -2147483648.
Constraints:
0 <= s.length <= 200
s
consists of English letters (lower-case and upper-case), digits (0-9
),' '
,'+'
,'-'
, and'.'
.
Sol
所以用之前的code來po
def my_atoi(str)
str = /[^\s]+/.match(str).to_s
parsed = /^[\+\-]?[0-9]+/.match(str).to_s
return 0 if parsed.empty?
parsed = parsed.to_i
if parsed > 2147483647
return 2147483647
elsif parsed < -2147483648
return -2147483648
else
return parsed
end
end