ListNode* divide_conquer(vector<ListNode*>& lists, int i, int j) {
// base case: only one or two lists left
if (i == j)
return lists[i];
if (i + 1 == j)
return merge2Lists(lists[i], lists[j]);
// Recursive: partion into two parts, [i, mid] and [mid+1, j]
// sort each part with divide_conquer(), and then merge them
int mid = i + (j - i) / 2;
return merge2Lists(divide_conquer(lists, i, mid), divide_conquer(lists, mid + 1, j));
}
struct PointArray* closest_pair(char *filename){
struct Connection *conn = File_open(filename, "rt");
struct PointArray *point_array = Connection_process(conn);
Connection_close(conn);
struct PointArraySplitted *split_array = split_point_array(point_array);
struct OrderedPointArray *ordered1 = malloc(sizeof(struct OrderedPointArray));
ordered1->x_ordered = split_array->array1;
ordered1->y_ordered = split_array->array1;
struct OrderedPointArray *ordered2 = malloc(sizeof(struct OrderedPointArray));
ordered2->x_ordered = split_array->array2;
ordered2->y_ordered = split_array->array2;
struct PointArray *result;
struct OrderedPointArray *result1 = split_sort(ordered1);
struct OrderedPointArray *result2 = split_sort(ordered2);
struct OrderedPointArray *result_merged = merge_point_array(result1, result2);
divide_conquer(result_merged->x_ordered, result_merged->y_ordered);
return result;
}
ListNode* mergeKLists(vector<ListNode*>& lists) {
if (lists.empty()) return NULL;
return divide_conquer(lists, 0, lists.size() - 1);
}
