Suppose there are n cities and m roads between the cities. Each city i currently has a of ai people, but we want to change its population to bi by moving people to different cities. Each person can either stay in the city they are currently in, or move to a neighboring city; that is, if the person is currently in city i, and (i,j) is a road connecting city i to city j, then the person can either stay in i or move to j. Give an algorithm to determine whether it is possible to move people to satisfy the problem re- quirements