DEV Community

plusOne Array of Integers in Javascript

Kurapati Mahesh on April 30, 2022

Increment the large integer by one and return the resulting array of digits. Example: Input: digits = [1,2,3] Output: [1,2,4] Explanation: The ar...
Read full post
Collapse
 
alexstaroselsky profile image
Alexander Staroselsky •

It’s important to remember that this is an interview question and they will press you on different ways to achieve this. Even if you use a BigInt and solve the question, depending on the level they will ask you to solve it without BigInt as well as explain the time and space complexity of your answer. So knowing how to do it with a loop and without string manipulation will likely be very important.

Collapse
 
frankwisniewski profile image
Frank Wisniewski •

another classic way

  const plusOne = (a, i=a.length-1) => {
    while (a[i]!=undefined){
      if (a[i] != 9){
        a[i]++;
        return a
      }
      a[i]=0
      i--
    }
    return [...[1],...a] 
  }
Enter fullscreen mode Exit fullscreen mode
Collapse
 
frankwisniewski profile image
Frank Wisniewski • 
  const plusOne = arr => (parseInt(arr.join(''))+1).toString().split('')

  console.log(plusOne([1,2,3,9]))
  console.log(plusOne([9]))
Enter fullscreen mode Exit fullscreen mode
Collapse
 
urstrulyvishwak profile image
Kurapati Mahesh •

Cool one. Thanks. But this fails in case of large arrays like..

[3,4,5,6,7,8,,1,2,3,1,2,3,4,5,6,7,8,8,4,3,2,5,6,7].

Collapse
 
frankwisniewski profile image
Frank Wisniewski • • Edited

you wrote integer...sorry

  const plusOne = arr => (BigInt(arr.join(''))+1n).toString().split('')

  console.log(plusOne([1,2,3,9]))
  console.log(plusOne([9]))
  console.log(plusOne([3,4,5,6,7,8,1,2,3,1,2,3,4,5,6,7,8,8,4,3,2,5,6,9,3,3,3,3,9]))
Enter fullscreen mode Exit fullscreen mode
Collapse
 
lexlohr profile image
Alex Lohr • 
const plusOne = (v) => [...(+v.join('') + 1).toString()]
Enter fullscreen mode Exit fullscreen mode
Collapse
 
urstrulyvishwak profile image
Kurapati Mahesh •

Number conversion fails in case of large numbers. But, yeah that is worst case. Cool one Alex. Much more simplified.

Collapse
 
lexlohr profile image
Alex Lohr • • Edited

Otherwise, we can use recursion:

const plusOne = (v, i) => i === undefined
  ? plusOne(v, v.length - 1)
  : v[i] < 9
  ? (v[i]++, v)
  : i === 0
  ? [1, 0, ...v.slice(1)]
  : ((v[i] = 0), plusOne(v, i - 1))
Enter fullscreen mode Exit fullscreen mode

I love recursion for cases like this, because it makes the different branches really obvious.

Collapse
 
frankwisniewski profile image
Frank Wisniewski •

plusOne([3,4,5,6,7,8,1,2,3,1,2,3,4,5,6,7,8,8,4,3,2,5,6,9,3,3,3,3,9])
….

Collapse
 
frankwisniewski profile image
Frank Wisniewski •

missing convert...

const plusOne = arr = (BigInt(arr.join(''))+1n).toString().split('').map(Number)
Enter fullscreen mode Exit fullscreen mode
Collapse
 
urstrulyvishwak profile image
Kurapati Mahesh •

Good. One. I think each time array needs to be converted completely even though the last digit is 9 or not.

any how, its simplified thanks.