8. String to Integer (atoi)

Problem

https://leetcode.com/problems/string-to-integer-atoi/

Implement atoi to convert a string to an integer.

Requirements for atoi:

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.

The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.

If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

Solution

Magical JavaScript built-in function!

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
    const INT_MAX = 2147483647
    const INT_MIN = -2147483648

    let num = parseInt(str)
    if (num) {
        if (num > INT_MAX) { return INT_MAX }
        if (num < INT_MIN) { return INT_MIN }
        return num
    }

    return 0
};

Well, if parseInt is forbidden in this case, we can still take advantage of other handy features.

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
    if (typeof str !== 'string') {
        str = str.toString()
    }

    const INT_MAX = 2147483647
    const INT_MIN = -2147483648

    let result = str.match(/^\s*([\+\-]?\d+)/)
    if (result) {

        // Magical Convert
        let num = result[1] * 1

        if (num > INT_MAX) { return INT_MAX }
        if (num < INT_MIN) { return INT_MIN }
        return num
    }

    return 0
};