Using coords instead of value in lowest point determination

puzzles/day09.py

@@ -31,13 +31,13 @@ class Heightmap:
                 elif y != max_y and self.heightmap[y+1][x] <= value:
                     continue
 
-                self.low_point_values.append(value)
+                self.low_point_values.append((x,y))
 
     def calculate_risk_score(self):
         if self.low_point_values is None:
             self.find_low_points()
 
-        return sum(value+1 for value in self.low_point_values)
+        return sum(self.heightmap[coords[1]][coords[0]]+1 for coords in self.low_point_values)
 
 
 def part1(inputs:   List[int]) -> int: