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DIY: Range Sum Query 2D — Immutable

Explore how to implement the NumMatrix class to handle range sum queries on a 2D matrix using immutable data structures. Learn to initialize the matrix and write the sumRegion method for calculating sums within given coordinates, preparing you for related coding interview problems.

Problem statement

Given an m * n matrix, you need to handle multiple queries of the following type:

Calculate the sum of the elements of the matrix inside the rectangle defined by its upper left corner, (row1,col1)(row1, col1) ...