1 Leetcode Java: Two Sum – Medium Problem. Given an array of integers, return indices of the two numbers such that they add up to a specific target. 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). Range Sum Query 2D The above rectangle (with the red border) is defined by (row1, col1) = (2, 1) and (row2, col2) = (4, 3), which contains sum = 8. Example: Given matrix = [[3, 0, 1, 4, 2],