public void update(int row, int col, int val) {
        int delta = val - matrix[row][col];
        matrix[row][col] = val;
        for (int i = col + 1; i <= cols; i++) {
            prefixSum[row][i] += delta;
        }
    }
Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner
(row1, col1) and lower right corner (row2, col2).

https://leetcode.com/problems/range-sum-query-2d-mutable/
src/com/interview/multiarray/Mutable2DSumRangeQuery.java