Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

The update(i, val) function modifies nums by updating the element at index i to val.

Example:

Given nums = [1, 3, 5]

sumRange(0, 2) -> 9

update(1, 2)

sumRange(0, 2) -> 8

Note:

1. The array is only modifiable by the update function.
2. You may assume the number of calls to update and sumRange function is distributed evenly.

class NumArray

  {

  public:

      NumArray(vector<int> &nums)

      {

          sums.push_back();

          for (int i = ; i < nums.size(); i++)

          {

              sums.push_back(sums[i] + nums[i]);

             values.push_back(nums[i]);

         }

     }

     void update(int i, int val)

     {

         int diff = val - values[i];

         for (int k = i + ; k < sums.size(); k++)

             sums[k] = sums[k] + diff;

         values[i] = val;

     }

     int sumRange(int i, int j)

     {

         return sums[j + ] - sums[i];

     }

 private:

     vector<int> sums;

     vector<int> values;

 };