// This was my original solution.
public int[] plusOne(int[] digits) {
        int j = digits.length-1;
        int res = digits[j]+1;
        int carryover = res/10;
        digits[j--] = res%10;
        while(j>=0){
            res = digits[j]+carryover;
            digits[j] = res%10;
            carryover = res/10;
            j--;
        }
        if (j<0 && carryover !=0){
            //create new array
            int[] nd = new int[digits.length+1];
            nd[0] =carryover;
            for(int i=1;i<nd.length; i++){
                nd[i] = digits[i-1];
            }
            return nd;
        }
        return digits;
    }


//This can be simplified further as follows.
public int[] plusOne(int[] digits) {
  for(int i=digits.length-1; i>=0; i--){
    if(digits[i]+1<=9){
      digits[i]++;
      return digits;
    }
      digits[i]=0;
  }
  // this case only occurs if the input array is like  9999
  int[] newarr = new int[digits.length()+1];
  newarr[0]=1;
  return newarr;
}