Add Strings

Description

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

Solution(javascript)

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings =  (num1, num2) => {
  const reversedNum1 = num1.split('').reverse()
  const reversedNum2 = num2.split('').reverse()
  const { shorter, longer } = reversedNum1.length < reversedNum2.length
    ? { shorter: reversedNum1, longer: reversedNum2 }
    : { shorter: reversedNum2, longer: reversedNum1 }

  let rem = 0
  let result = longer.reduce((acc, digit1, index) => {
    const total = parseInt(digit1, 10) + (parseInt(shorter[index], 10) || 0) + rem
    if (total >= 10) {
      rem = 1
    } else {
      rem = 0
    }
    return [
      ...acc,
      total >= 10 ? total - 10 : total,
    ]
  }, [])
  result = rem === 1 ? [...result, rem] : result
  return result.reverse().join('')
}