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7. Plus One

easyAsked at GoDaddy

Increment a large integer represented as an array of digits by one.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

You are given a non-empty array of decimal digits representing a non-negative integer. Increment the integer by one and return the resulting array of digits.

Constraints

  • 1 <= digits.length <= 100
  • 0 <= digits[i] <= 9
  • No leading zero except number 0 itself

Examples

Example 1

Input
digits = [1,2,3]
Output
[1,2,4]

Example 2

Input
digits = [9,9]
Output
[1,0,0]

Approaches

1. BigInt convert

Convert to BigInt, add 1, convert back to digit array.

Time
O(n)
Space
O(n)
return (BigInt(digits.join(''))+1n).toString().split('').map(Number);

Tradeoff:

2. Right to left carry

Walk from the last digit; carry only while digit was 9.

Time
O(n)
Space
O(1)
function plusOne(digits) {
  for (let i = digits.length - 1; i >= 0; i--) {
    if (digits[i] < 9) {
      digits[i]++;
      return digits;
    }
    digits[i] = 0;
  }
  return [1, ...digits];
}

Tradeoff:

GoDaddy-specific tips

GoDaddy treats this as a model for incrementing serial numbers in DNS SOA records, where 32-bit overflow handling and carry behavior matter.

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Output

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