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 = "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.
Example 4:
Input: s = "words and 987" Output: 0 Explanation: 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 = "-91283472332" Output: -2147483648 Explanation: 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'.'
.
Solution 1:
/**
* @param {string} s
* @return {number}
*/
var myAtoi = function(s) {
const len = s.length;
let max = 2147483647;
let min = -2147483648;
let numberMatch = /^[\d ()+-]+$/;
for (let i = 0, j = i; i < len; i++) {
let current = s[i];
if (current != " " && !current.match(numberMatch)) {
return 0;
} else if (current != " " && current.match(numberMatch)) {
let result = "";
while (j < len && current.match(numberMatch)) {
result += s[j];
j++;
}
let output = parseInt(result);
if (isNaN(output)) return 0;
else if (output > max) return max;
else if (output < min) return min;
else return output;
}
}
return 0;
};
Solution 2:
/**
* @param {string} s
* @return {number}
*/
var myAtoi = function(s) {
let i = 0;
let sign = 1;
let res = 0;
let len = s.length;
let INT_MAX = 2147483647;
let INT_MIN = - INT_MAX - 1;
// skip all space
while (s[i] === ' ') i++;
// check sign
if (s[i] === '+' || s[i] === '-') {
sign = s[i] === '+' ? 1 : -1;
i++;
}
while (s[i] >= '0' && s[i] <= '9') {
res = (res * 10) + (s[i] - 0);
if (sign === 1 && res > INT_MAX) return INT_MAX;
if (sign === -1 && res > INT_MAX + 1) return INT_MIN;
i++;
}
return res * sign;
};