[Happy DSA] 如何对单链表进行快速排序

之前有一篇文章介绍了glib库中单双向链表的排序采用了归并排序，并且不需要额外的空间，这篇文章将介绍c-algorithms库中单双向链表的快速排序过程：

通常快速排序算法都是施行于数组，但它也可以作用于单链表（这里以单向链表为例）。

原理跟数组快速排序是一样的，先partition，然后再递归的解决子单链表的快速排序。

以下是从c-algorithms代码中摘下来的代码段:

static SListEntry *slist_sort_internal(SListEntry **list,                                        SListCompareFunc compare_func){     SListEntry *pivot;     SListEntry *rover;     SListEntry *less_list, *more_list;     SListEntry *less_list_end, *more_list_end;          /* If there are less than two entries in this list, it is     * already sorted */     if (*list == NULL || (*list)->next == NULL) {          return *list;     }     /* The first entry is the pivot */     pivot = *list;     /* Iterate over the list, starting from the second entry.  Sort     * all entries into the less and more lists based on comparisons     * with the pivot */     less_list = NULL;     more_list = NULL;     rover = (*list)->next;     while (rover != NULL) {          SListEntry *next = rover->next;          if (compare_func(rover->data, pivot->data) < 0) {               /* Place this in the less list */               rover->next = less_list;               less_list = rover;          } else {               /* Place this in the more list */               rover->next = more_list;               more_list = rover;          }          rover = next;     }     /* Sort the sublists recursively */     less_list_end = slist_sort_internal(&less_list, compare_func);     more_list_end = slist_sort_internal(&more_list, compare_func);     /* Create the new list starting from the less list */     *list = less_list;     /* Append the pivot to the end of the less list.  If the less list     * was empty, start from the pivot */     if (less_list == NULL) {          *list = pivot;     } else {          less_list_end->next = pivot;     }     /* Append the more list after the pivot */     pivot->next = more_list;     /* Work out what the last entry in the list is.  If the more list was      * empty, the pivot was the last entry.  Otherwise, the end of the      * more list is the end of the total list. */     if (more_list == NULL) {          return pivot;     } else {          return more_list_end;     }}void slist_sort(SListEntry **list, SListCompareFunc compare_func){     slist_sort_internal(list, compare_func);}