I’m experiencing a strange issue with two similar pieces of C++ code that are supposed to perform the same task but yield different results.
The problem is around the inner loop statement .

I was trying to solve QUESTION.

While implementing the solution,I came across this issue:-

        int n;
        cin >> n;
        vector<int> arr(n);
        REP(i, 0, n){
            cin >> arr[i];
        }

        vector<int> dup = arr;
        int maxVal = INT_MIN;
        REP(i, 0, n){
            if (arr[i] > maxVal){
                maxVal = arr[i];
            }
            if (arr[i] < maxVal){
                arr[i] = maxVal;
            }
        }

        REP(i, 0, n){
            dup[i] = arr[i] - dup[i];
        }

        int ans = 0;
        sort(dup.begin(), dup.end());

        REP(i, 0, n){
            if (dup[i] != 0){
                ans += (n - i + 1) * dup[i];

               //This inner loop

                for(int j = i; j < n; j++){
                    dup[j] -= dup[i];
                }
            }
        }
        cout << ans << "n";
    }
    return 0;

While I was able to get the correct result by replacing the inner loop with transform function ,but I am not able to understand why doesn’t this work .The code gives the same answer even after I remove the inner loop ,as if the inner loop is not even doing anything.

I am not a expert or something in codeforces but I have solved a good amount of problems involving loops and arrays ,here I am really clueless about the issue .

Could someone help me understand why the first version of the code doesn’t produce the correct result? Is there a logical error in how I am updating the dup vector?

Also this the transform function which I am talking about :-

transform(dup.begin() + i, dup.end(), dup.begin() + i,
                         [value = dup[i]](int x) { return x - value; });