Before revision:  The problem was previously solved in O(n ) time using O(1) variables for working space, where denotes the cardinality of reflex vertices of \mathcal P in the output .
After revision:  The problem was previously solved in O(n ) time using O(1) variables for working space, where denotes the cardinality of reflex vertices of \mathcal P ) -time and O(n) -variables space. In a newer research, the visibility area of a point be computed in O(n) -time, using O(\sqrt{n .