Count how many times a carry operation is performed while adding two numbers

numberOfCarryOperations.js

function numberOfCarryOperations(a, b) {
  const aDigits = String(a).split('').reverse()
  const bDigits = String(b).split('').reverse()
  const maxDigits = aDigits.length > bDigits.length ? aDigits : bDigits
  const minDigits = maxDigits === aDigits ? bDigits : aDigits
  /// console.log({a, b, maxDigits, minDigits})

  let carry = 0
  const carryCount = maxDigits.reduce((c, d, i) => {
    const dA = Number(d) || 0
    const dB = Number(minDigits[i]) || 0
    let r = carry + dA + dB

    carry = 0
    if (r >= 10) {
      /// r -= 10
      c += 1
      carry = 1
    }
    /// console.log({dA, dB, c, r})

    return c
  }, 0)

  return carryCount
}

console.log(numberOfCarryOperations(123, 456)) // 0
console.log(numberOfCarryOperations(555, 555)) // 3
console.log(numberOfCarryOperations(900, 11)) // 0
console.log(numberOfCarryOperations(145, 55)) // 2
console.log(numberOfCarryOperations(0, 0)) // 0
console.log(numberOfCarryOperations(1, 99999)) // 5
console.log(numberOfCarryOperations(999045, 1055)) // 5
console.log(numberOfCarryOperations(101, 809)) // 1
console.log(numberOfCarryOperations(189, 209)) // 1

numberOfCarryOperationsArray.js

const toDigit = d => Number(d) || 0

function numberOfCarryOperations(numbs) {
  numbs = numbs.map(n => String(n).split('').reverse())
  const maxDigitsLen = Math.max(...numbs.map(n => n.length))
  const maxDigitsIdx = numbs.findIndex(n => n.length === maxDigitsLen)
  const maxDigits = numbs.splice(maxDigitsIdx, 1)[0]
  /// console.log({maxDigits, numbs})

  let carry = 0 // first carry
  const carryCount = maxDigits.reduce((c, d, i) => {
    let r = carry + toDigit(d) + numbs.reduce((t, n) => t + toDigit(n[i]), 0)
    
    carry = 0 // next carry
    while (r - 10 >= 0) {
      r -= 10
      c += 1
      carry += 1
    }
    /// console.log({c, carry, r})

    return c
  }, 0)

  return carryCount
}

console.log(numberOfCarryOperations([123, 456, 0])) // 0
console.log(numberOfCarryOperations([123, 456, 999])) // 3
console.log(numberOfCarryOperations([555, 555])) // 3
console.log(numberOfCarryOperations([900, 11])) // 0
console.log(numberOfCarryOperations([145, 55])) // 2
console.log(numberOfCarryOperations([0, 0])) // 0
console.log(numberOfCarryOperations([1, 99999])) // 5
console.log(numberOfCarryOperations([999045, 1055])) // 5
console.log(numberOfCarryOperations([101, 809])) // 1
console.log(numberOfCarryOperations([189, 209])) // 1
console.log(numberOfCarryOperations([999, 999, 999])) // 6

numberOfCarryOperationsNumbers.js

function digitForIdx(num, i) {
  return Math.floor((num / Math.pow(10, i)) % 10)
}

function numberOfCarryOperations(a, b) {
  const maxLen = String(Math.max(a, b)).length

  const carry = [0]
  for (let i = 0; i < maxLen; i++) {
    const r = carry[i] + digitForIdx(a, i) + digitForIdx(b, i)
    carry[i + 1] = ((r >= 10) ? 1 : 0)
  }

  return carry.filter(c => c).length
}

console.log(numberOfCarryOperations(123, 456)) // 0
console.log(numberOfCarryOperations(555, 555)) // 3
console.log(numberOfCarryOperations(900, 11)) // 0
console.log(numberOfCarryOperations(145, 55)) // 2
console.log(numberOfCarryOperations(0, 0)) // 0
console.log(numberOfCarryOperations(1, 99999)) // 5
console.log(numberOfCarryOperations(999045, 1055)) // 5
console.log(numberOfCarryOperations(101, 809)) // 1
console.log(numberOfCarryOperations(189, 209)) // 1

numberOfCarryOperationsSimpleForLoop.js

function toDigit(a) { return Number(a) || 0 }

function numberOfCarryOperations(a, b) {
  a = String(a).split('').reverse()
  b = String(b).split('').reverse()

  const maxLen = Math.max(a.length, b.length)
  const carry = []
  
  for (var i = 0; i < maxLen; i++) {
    // console.log(toDigit(a[i]), toDigit(b[i]), toDigit(carry[i-1]))
    carry[i] = (toDigit(a[i]) + toDigit(b[i]) + toDigit(carry[i-1])) > 9
      ? 1
      : 0
  }

  return carry.filter(v => v).length
}

console.log(numberOfCarryOperations(123, 456)) // 0
console.log(numberOfCarryOperations(555, 555)) // 3
console.log(numberOfCarryOperations(900, 11)) // 0
console.log(numberOfCarryOperations(145, 55)) // 2
console.log(numberOfCarryOperations(0, 0)) // 0
console.log(numberOfCarryOperations(1, 99999)) // 5
console.log(numberOfCarryOperations(999045, 1055)) // 5
console.log(numberOfCarryOperations(101, 809)) // 1
console.log(numberOfCarryOperations(189, 209)) // 1