The usual algorithms for topological sorting have running time linear in the number of nodes plus the number of edges, asymptotically, O(E+V)

We update the value at start index, because it will be used in the future when we are adding up the values for the sum at each index between start index and end index(both inclusive). We update the negative value at the end index + 1, because the positive value of it should be only added at its previous indices (from start index to end index). Thus, when we accumulate the sum at the end for each index, we will get the correct values for each index. If the end index is the last index in the resulting array, we don’t have to do the end index + 1part, because there is no more index after the last index and there will be no error when we accumulate the sum.