8 - String to Integer (atoi)\.

Medium

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 is 0. Change the sign as necessary (from step 2).

• If the integer is out of the 32-bit signed integer range <code>-2³¹, 2³¹ - 1</code>, then clamp the integer so that it remains in the range. Specifically, integers less than <code>-2³¹</code> should be clamped to <code>-2³¹</code>, and integers greater than <code>2³¹ - 1</code> should be clamped to <code>2³¹ - 1</code>.

• 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 '.'.