Move sort_cells to operator< of Cell class

main.cpp

@@ -67,6 +67,10 @@ public:
 
         possible_values = possibilities;
     }
+
+    bool operator<(const Cell &other) {
+        return possible_values.size() < other.possible_values.size(); 
+    }
 };
 
 class Sudoku {
@@ -101,12 +105,7 @@ public:
             cell.update_possible_values();
         }
 
-        std::make_heap(heap.begin(), heap.end(), sort_cells);
-    }
-
-    // TODO: Turn this into a member of Cell as opterator<
-    static bool sort_cells(const Cell& a, const Cell& b) {
-        return a.possible_values.size() < b.possible_values.size(); 
+        std::make_heap(heap.begin(), heap.end());
     }
 
     // Update the possible values which a cell can take for every cell in the heap
@@ -115,12 +114,12 @@ public:
             cell.update_possible_values();
         }
 
-        std::sort_heap(heap.begin(), heap.end(), sort_cells);
+        std::sort_heap(heap.begin(), heap.end());
     }
 
     // Returns the best cell in the heap (the one with the most obvious choice)
     Cell get_next_best_empty_cell() {
-		std::pop_heap(heap.begin(), heap.end(), sort_cells);
+		std::pop_heap(heap.begin(), heap.end());
 		Cell c = heap.back();
         heap.pop_back();
         
@@ -179,7 +178,7 @@ public:
 
         // Put the cell back into the heap -- it couldn't be used for any valid solution, so we'll need it somewhere else later
         heap.push_back(cell);
-        std::push_heap(heap.begin(), heap.end(), sort_cells);
+        std::push_heap(heap.begin(), heap.end());
 
         return false;
     }