1. An elevation map is of the type List [List [int]], and moreover, the length of an elevation map equals the length of elements within the elevation map. An elevation map will only contain positive numbers. An example of an elevation map is: valid.nap- [01,2,3),(4,5,6],7,8,91 It may be more intuitive to view the map as: valid aap - [1,2,3], [7,8,911 The following two examples are not elevation maps (note the length of all the lists in each) invalid.nap1 [01,2,3, 4,5, (6,7,8,91 invalid.nap2 01,2,3), 4,5,6],07,8,9), 010,1,121 2. A ce is of the type Listlint] and has a length of 2. All values in a cell will be greater than or equal to 0. Within an elevation map m, we say cell i,j) as a shorthand for mlui]. We also say cell i,j] is adjacent to cell n, m) if and only if In, m equals one of: 3. Within an elevation mapm, el [i,j is a sink if for all adjacent cells In, m], mil Smnm. With the physical interpretation of an elevation map in mind, water would collect in sinks since there is no less elevated area in the immediate vicinity for the water to flow to