0008-string-to-integer-atoi.js

/**
 * 8. String to Integer (atoi)
 * https://leetcode.com/problems/string-to-integer-atoi/
 * Difficulty: 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 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 is 0. 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
 *   than 231 - 1 should be clamped to 231 - 1.
 * - Return the integer as the final result.
 */

/**
 * @param {string} s
 * @return {number}
 */
var myAtoi = function(s) {
  const parsed = +(s.trim().match(/^[-+]?\d+/g) || [0])[0];
  const clamped = Math.min(Math.max(parsed, (-2)**31), 2**31 - 1);

  return clamped;
};