String to Integer (atoi), Medium

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:

Whitespace: Ignore any leading whitespace (" ").

Signedness: Determine the sign by checking if the next character is '-' or '+', assuming positivity if neither present.

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.

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.

Solution, Typescript

function myAtoi(s: string): number {
    s = s.trim();   // remove whitespace

    let sign = 1;
    let startIdx = 0;
    let endIdx = s.length - 1;

    // detect signedneess
    if(s.charAt(0) === "-") {
        sign = -1;
        startIdx++;
    } else if(s.charAt(0) === "+") {
        startIdx++;
    }

    // skip leading zeros
    while(true) {
        if(s.charAt(startIdx) !== "0") {
            break
        }
        startIdx++;
    }

    let val = 0;
    let placeVal = 1;
    for(let i = endIdx; i >= startIdx; i--) {

        let digit = digitConvert(s.charAt(i));
        if(digit == -1) {
            val = 0;
            placeVal = 1;
            continue;
        }
        val += digit * placeVal;
        placeVal *= 10;
    }

    val = sign*val;

    // console.log(val)
    val = Math.max(val, -(2**31));
    // console.log(val, (-2)**31)
    val = Math.min(val, 2**31 - 1);
    // console.log(val, 2**31 - 1)

    return val;
};

function digitConvert(s: string): number {
    switch(s) {
        case "0":
            return 0;
        case "1":
            return 1;
        case "2":
            return 2;
        case "3":
            return 3;
        case "4":
            return 4;
        case "5":
            return 5;
        case "6":
            return 6;
        case "7":
            return 7;
        case "8":
            return 8;
        case "9":
            return 9;
        default:
            return -1;
    }