What is the difference between the following two codes?

You are given an array A of size N. Your task is to find the minimum number of operations needed to convert the given array to 'Palindromic Array'.

Palindromic Array: [23,15,23] is a ‘Palindromic Array’ but [2,0,1] is not.

The only allowed operation is that you can merge two adjacent elements in the array and replace them with their sum.

Input: The first line of input contains an integer T denoting the number of test cases. The first line of each test case is N, where N is the size of array. The second line of each test case contains N space separated integers which is the input for the array.

Output: Output the minimum number of operations required to make the given array a palindromic array.

Constraints: 1<=T<=100 1<=N<=100

Example: Input: 2 5 3 2 3 3 5 4 5 3 3 4 Output: 1 3

Explanation: For Test Case 1: [3 2 3 3 5] after merging the 1st two elements 3 and 2, we get the array as [5 3 3 5] which is a palindrome, hence only 1 operation is needed.

What is the difference between the following two codes if I first write a[i+1]+=a[i] and then increment i (i.e. i++) and if I first increment i (i.e i++) and then perform a[i]+=a[i-1]??

My solution This is working but the commented part of the else if condition is not working.

import java.util.*;
import java.lang.*;
import java.io.*;
class hello
 {
    public static void main (String[] args)
     {
     //code
     Scanner sc=new Scanner(System.in);
     int t=sc.nextInt();
     for(int k=0;k<t;k++)
     {
         int c=0;
         int n=sc.nextInt();
         int i=0,j=n-1;
         int a[]=new int[n];
         for(int z=0;z<n;z++)
         {
             a[z]=sc.nextInt();
         }
            while(i<=j)
            {
             if(a[i]==a[j])
             {
                i++;
                j--;
             }
             else if(a[i]<a[j]) 
             {
                 i++;
                 a[i]+=a[i-1];               //why not a[i+1]=a[i]+a[i+1];
                 c++;                       // and then i++;
             }
             else
             {
                 j--;
                 a[j]+=a[j+1];                      //same question goes for this
                 c++;
             }
            }
             System.out.println(c);
         }
     }
    }