Calculate sum of all elements in a sub-matrix in constant time

Given a M x N matrix and two coordinates (p, q) and (r, s) which represents top-left and bottom-right coordinates of a sub-matrix of the given matrix, calculate the sum of all elements present in the sub-matrix in O(1) time. Here, 0 < = p < r < M and 0

Find Probability that a Person is Alive after Taking N steps on an Island

Given an island in the form of square matrix and a point inside the matrix where a person is standing. The person is allowed to move one step in any direction (right, left, top, down) on the matrix. If he steps outside the matrix, he dies. Calculate the probability that he is alive after he …