String to Integer (atoi)

Problem Description

Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer.

The algorithm for myAtoi(string s) is as follows:

1. Whitespace: Ignore any leading whitespace (" ").
2. Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present.
3. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read, then the result is 0.
4. Rounding: If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then round the integer to remain in the range. Specifically, integers less than -231 should be rounded to -231, and integers greater than 231 - 1 should be rounded to 231 - 1.

Return the integer as the final result.

Example 1:

The underlined characters are what is read in and 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)
           ^

Example 2:

Step 1: "   -042" (leading whitespace is read and ignored)
            ^
Step 2: "   -042" ('-' is read, so the result should be negative)
             ^
Step 3: "   -042" ("042" is read in, leading zeros ignored in the result)
               ^

Example 3:

Step 1: "1337c0d3" (no characters read because there is no leading whitespace)
         ^
Step 2: "1337c0d3" (no characters read because there is neither a '-' nor '+')
         ^
Step 3: "1337c0d3" ("1337" is read in; reading stops because the next character is a non-digit)
             ^

Example 4:

Step 1: "0-1" (no characters read because there is no leading whitespace)
         ^
Step 2: "0-1" (no characters read because there is neither a '-' nor '+')
         ^
Step 3: "0-1" ("0" is read in; reading stops because the next character is a non-digit)
          ^

Example 5:

Constraints:

• 0 <= s.length <= 200
• s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'.

Solution (JavaScript)

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
    const INT_MAX = Math.pow(2, 31) - 1;
    const INT_MIN = Math.pow(2, 31) * -1;
    
    const i = parseInt(str.trim().split(' ')[0]);
    
    if(isNaN(i)) return 0;
    if(i < INT_MIN) return INT_MIN;
    if(i > INT_MAX) return INT_MAX;
    return i;
};