嵌入式学习第三十天！（单向链表练习）

1. 单向链表的逆序：

int Is_Empty_Link(LINK_LIST *plist)
{return plist->phead == NULL;
}void Reverse_Link(LINK_LIST *plist)
{LINK_NODE *ptmp = plist->phead;LINK_NODE *pinsert = NULL;plist->phead = NULL;if(Is_Empty_Link(plist)){return;}else{while(ptmp != NULL){pinsert = ptmp;ptmp = ptmp->pnext;pinsert->pnext = plist->phead;plist->phead = pinsert;}}return;
}

        在这里的逆序，利用了头插法的思想，因为利用头插法插入数据，数据是逆序插入的，最后插入的数据在最前面，最先插入的数据在最后面，那么逆序也可以使用这个思想。

2. 找到单向链表中的中间结点

LINK_NODE *Find_Center_Link(LINK_LIST *plist)
{LINK_NODE *pfast = plist->phead;LINK_NODE *pslow = plist->phead;while(pfast != NULL){pfast = pfast->pnext;if(pfast == NULL){break;}pfast = pfast->pnext;pslow = pslow->pnext;}return pslow;
}

        采用链表中比较常用的快慢指针法，那么快指针每次走两步，慢指针每次走一步，当快指针走到等于NULL的时候，慢指针刚好走到了中间结点，但是在这个地方，如果遇到偶数个结点的单向链表，那么得到的中间结点为中间的后一个结点。如果想要中间结点的前一个结点的话，那么需要修改一下判断条件：

LINK_NODE *Find_Center_Link(LINK_LIST *plist)
{LINK_NODE *pfast = plist->phead;LINK_NODE *pslow = plist->phead;while(1){pfast = pfast->pnext;if(pfast == NULL){break;}pfast = pfast->pnext;if(pfast == NULL){break;}pslow = pslow->pnext;}return pslow;
}

3. 找到单向链表的倒数第K个结点

LINK_NODE *Find_Last_K_Node(LINK_LIST *plist, int K)
{LINK_NODE *pfast = plist->phead;LINK_NODE *pslow = plist->phead;for(int i = 0; i < K; i++){if(pfast == NULL){return NULL;}pfast = pfast->pnext;}while(pfast != NULL){pfast = pfast->pnext;pslow = pslow->pnext;}return pslow;
}

        同样可以使用快慢指针法的思想，让快指针先走K步，然后再让快指针和慢指针同时一起走，当快指针走到等于NULL的时候，那么慢指针刚好比慢指针少K步，也就是倒数第K个结点

4. 删除单向链表的某个结点

int Delete_Link_Node(LINK_LIST *plist, DATA_TYPE data)
{if(Is_Empty_Link(plist)){return 0;}LINK_NODE *pfree = plist->phead;LINK_NODE *ppre = NULL;int del_cnt = 0;while(pfree != NULL){if(pfree->data == data){if(pfree == plist->phead){plist->phead = pfree->pnext;free(pfree);pfree = plist->phead;}else{ppre->pnext = pfree->pnext;free(pfree);pfree = ppre->pnext;}plist->curlen--;del_cnt++;}else{ppre = pfree;pfree = pfree->pnext;}}return del_cnt;
}

        可以发现这段代码可以将所有数据为data的链表结点都删除了，如果只想删除第一个的话，那就在找到第一个数据为data的结点以后，将结点free掉，然后直接return，那么程序就实现了只删除第一个。

5. 实现单向链表的升序排序（插入排序的思想）

int Insert_Sort_Link(LINK_LIST *plist)
{LINK_NODE *pinsert = NULL;LINK_NODE *ptmp = plist->phead;plist->phead->pnext = NULL;while(ptmp != NULL){pinsert = ptmp;ptmp = ptmp->pnext;if(pinsert->data <= plist->phead->data){pinsert->pnext = plist->phead;plist->phead = pinsert;}else{	LINK_NODE *perg = plist->phead;while(perg->pnext != NULL && pinsert->data >= perg->pnext->data){perg = perg->pnext;}pinsert->pnext = perg->pnext;perg->pnext = pinsert;}}return 0;
}