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'.'
.
Solutions
✅Time: O(n)
✅Space: O(1)
C++
class Solution {
public:
int myAtoi(string s) {
trim(s);
if (s.empty())
return 0;
const int sign = s[0] == '-' ? -1 : 1;
if (s[0] == '+' || s[0] == '-')
s = s.substr(1);
long num = 0;
for (const char c : s) {
if (!isdigit(c))
break;
num = num * 10 + (c - '0');
if (sign * num < INT_MIN)
return INT_MIN;
if (sign * num > INT_MAX)
return INT_MAX;
}
return sign * num;
}
private:
void trim(string& s) {
s.erase(0, s.find_first_not_of(' '));
s.erase(s.find_last_not_of(' ') + 1);
}
};
Java
class Solution {
public int myAtoi(String s) {
s = s.strip();
if (s.isEmpty())
return 0;
final int sign = s.charAt(0) == '-' ? -1 : 1;
if (s.charAt(0) == '+' || s.charAt(0) == '-')
s = s.substring(1);
long num = 0;
for (final char c : s.toCharArray()) {
if (!Character.isDigit(c))
break;
num = num * 10 + (c - '0');
if (sign * num <= Integer.MIN_VALUE)
return Integer.MIN_VALUE;
if (sign * num >= Integer.MAX_VALUE)
return Integer.MAX_VALUE;
}
return sign * (int) num;
}
}
Python
class Solution:
def myAtoi(self, s: str) -> int:
s = s.strip()
if not s:
return 0
sign = -1 if s[0] == '-' else 1
if s[0] in {'-', '+'}:
s = s[1:]
num = 0
for c in s:
if not c.isdigit():
break
num = num * 10 + ord(c) - ord('0')
if sign * num <= -2**31:
return -2**31
if sign * num >= 2**31 - 1:
return 2**31 - 1
return sign * num
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