plus-one.js

/**
 * Plus One
 *
 * Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
 *
 * You may assume the integer do not contain any leading zero, except the number 0 itself.
 *
 * The digits are stored such that the most significant digit is at the head of the list.
 *
 * Example 1:
 *
 * Input: [1,2,3]
 * Output: [1,2,4]
 * Explanation: The array represents the integer 123.
 *
 * Example 2:
 *
 * Input: [4,3,2,1]
 * Output: [4,3,2,2]
 * Explanation: The array represents the integer 4321.
 */

/**
 * @param {number[]} digits
 * @return {number[]}
 */
const plusOne = digits => {
  for (let i = digits.length - 1; i >= 0; i--) {
    if (digits[i] === 9) {
      digits[i] = 0;
    } else {
      digits[i]++;
      return digits;
    }
  }

  digits.unshift(1);
  return digits;
};

export default plusOne;