Plus One

/* 
*  Programmer     : Dhruv Patel
*  Problem Name   : Plus One
*  Used In        : Leetcode
*  Used As        : 66
*  Thoughts     => 
*  O(N)            We have to iterate from the last index to the first index of an array.Only,last index should
*                  be added digit 1.It's a naive approach what students do in a school. We simply carry forward
*                  the carry till the loop ends if the sum is greater than 9.
*                  To get the carry we divide sum / 10 and reduce sum by sum %= 10 formula
*                  If carry overflows than we simply check its value after the loop terminates and append to the list. 
*                  We reverse the list and return as an array.
*/
package solution;
import java.util.*;
import java.util.ArrayList;
import java.util.List;
public class Solution {
    public static int[] plusOne(int[] digits) {
       int carry = 0 ;
        List<Integer> list = new ArrayList<>();
        int sum = 0;
        Boolean flag = true;
        for(int i = digits.length-1 ; i >= 0 ; i--) {
            if(flag){    
                sum = digits[i] + carry + 1;
                flag = false;
            }else{
                sum = digits[i] + carry;
            }if(sum>9){
                    carry = sum/10;
                    sum = sum%10;
                }else{
                    carry = 0;
                }
                list.add(sum);
        }
        if(carry>0){
            list.add(carry);
        }
        //System.out.println("sum = " + sum);
        Collections.reverse(list);
        int ans[] = new int[list.size()];
        int x = 0 ;
        for(int i : list) {
            ans[x] = i;
            x++;
        }
        return ans;
    }
public static void main(String args[]) {
    int a[] = {1,0};
    int b[] = {1,0,-1,-1,-3};
    int c[] = {-9999999,-99,-999999999,-999999};
    System.out.println(Arrays.toString(plusOne(c)));
    }
}