This video explains a very important programming interview problem based on 2d matrix which is finding range sum on a 2D matrix. If this problem was on 1D array then we could have applied prefix sum or segment tree if updates were allowed. In this case, we don't have updates, so 2D prefix sum array can be built to solve the problem. This will take order of number of rows or columns time depending on how we build prefix sum array. The best approach however just does preprocessing once and we can solve each query in O(1) constant time. I have explained all the approaches one by one to solve the problem along with intuition and examples.
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15 фев 2022
