66. Plus One

A large integer is given as an array of its digits, most significant first, with no leading zeros. Return the digits of the integer plus one.

Scan from the right. A 9 becomes 0 and the carry moves on; the first digit below 9 just goes up by one and we are done. If every digit was 9, the answer is 1 followed by zeros.

1function plusOne(digits: number[]): number[] {
2  for (let i = digits.length - 1; i >= 0; i--) {
3    if (digits[i] < 9) { digits[i]++; return digits; }
4    digits[i] = 0;
5  }
6  return [1, ...digits];
7}