Leetcode 396. Rotate Function solution

Problem statement could be found @https://leetcode.com/problems/rotate-function/

Solution Approach-
Lets consider the numbers given in example [4,3,2,6] so we have following combinations
4 * 0 + 3* 1 + 2 *2 + 6 * 3
3 * 0 + 2 * 1 + 6 * 2 + 4 * 3
2 * 0 + 6 * 1 + 4 * 2 + 3 * 3
6 * 0 +  4 * 1 + 3 * 3 + 2 * 3

If one looks it closely it would seems like a sliding window for following array
4, 3,2,6,4,3,2

Above step means append  (n-1) elements to original vector.

Another optimization is  between first and second step, the difference is

In first step
Step 1. totalSum = 25
Step2. pSum = 3 +  2 + 6
Step 3. now in step2, total value has to be decreased by pSum as we shift left and now 4 * 3 has to be added, where 4 is the new element value & 3 (vector size -1).

At every slide of window these steps are applied



Following is the code

class Solution {
public:
   
    int maxRotateFunction(vector<int>& A) {
        if (A.size() == 0)
            return 0;
           
       
         if (A.size() == 1)
            return A[0]*0;
           
       int maxSum  = 0;
       int pSum = 0;
       int size = A.size();
     
       for (int i=0;i<size;i++) {
           maxSum = maxSum + (A[i] * i);
           if (i != 0 )
            pSum = pSum + A[i];
       }
       for (int i=0;i<size-1;i++){
           A.push_back(A[i]);
       }
      int gMax = maxSum;
    //  size = A.size();
      for (int i=1;i<size ;i++){
          //maxSum - pSum;
          maxSum  = maxSum - pSum + A[size+i-1] * (size - 1);
          pSum = pSum - A[i]  + A[i+size-1];
          if (maxSum > gMax)
            gMax = maxSum;
      }
      return gMax;
    }
};