Be careful when we have, say 99, we will need to create a new array to put 100. We only need to assign "1" to the first element since the default values of the remaining elements are "0".

```
public class Solution {
public int[] plusOne(int[] digits) {
for(int i = digits.length - 1; i >= 0; i--) {
digits[i] = (digits[i] + 1 != 10) ? digits[i] + 1 : 0;
if(digits[i] != 0) return digits;
}
int [] result = new int[digits.length + 1];
result[0] = 1;
return result;
}
}
```