S为指针,pre为直接前驱指针,next为直接后驱指针。非首尾结点,不需做额外判断和处理了。
1. S->pre = P->pre;
S->next = P;
P->pre = S;
2. P->next = P->next->next;
free(P->next->pre) ;
P->next->pre = P;
3. P->pre = P->pre->pre
free(P->pre->next) ;
P->pre->next = P;
4. P->pre->next = P->next;
P->next->pre = P->pre;
free(P) ;