public int sumRegion(int row1, int col1, int row2, int col2) {
        int sum = 0;
        for (int i = row1; i <= row2; i++) {
            sum += prefixSum[i][col2 + 1] - prefixSum[i][col1];
        }
        return sum;
    }
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