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 character 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 = "42"
Output: 42
Explanation: 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 = " -42"
Output: -42
Explanation:
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 words"
Output: 4193
Explanation:
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.
Constraints:
-
0 <= s.length <= 200
-
s
consists of English letters (lower-case and upper-case), digits (0-9
),' '
,'+'
,'-'
, and'.'
.
SOLUTION:
class Solution:
def clamp(self, val, MIN, MAX):
if val < MIN:
return MIN
if val > MAX:
return MAX
return val
def myAtoi(self, s: str) -> int:
MIN = -1 << 31
MAX = -MIN - 1
sign = None
val = None
for c in s:
if c == "+" or c == "-":
if val != None:
break
if sign == None:
sign = [-1, 1][c == "+"]
else:
return 0
elif 48 <= ord(c) < 58:
d = ord(c) - 48
val = 10 * (val or 0) + d
elif val == None and sign == None:
if c != " ":
return 0
else:
break
return self.clamp((sign or 1) * (val or 0), MIN, MAX)
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