The interviewer was very unprofessional. When I requested time to think, he couldn't stop talking. The questions he picked were very hard and advanced, requiring significant coding with advanced data structures. This approach isn't optimal for an interview and is very unprofessional.

Given an N x M matrix A of non-negative integers representing the height of each unit cell in a continent, the "Blue lake" touches the left and top edges of the matrix, and the "Red lake" touches the right and bottom edges.

Water can only flow in four directions (up, down, left, or right) from a cell to another one with height equal to or lower.

Find the number of cells from where water can flow to both the Blue and Red lake.