链表翻转。比如给出一个链表和一个数k，比如链表1→2→3→4→5→6，k=2，翻转后2→1→4→3→6→5

链表翻转

题目：链表翻转。给出一个链表和一个数k，比如链表1→2→3→4→5→6，k=2，翻转后2→1→4→3→6→5，若k=3,翻转后3→2→1→6→5→4，若k=4，翻转后4→3→2→1→5→6，用程序实现Node* RotateList(Node* list, size_t k). 提示：这个题是链表逆置的升级变型。

算法思想：

这个题是链表逆置的升级变型，我们可以将此链表先按照以k为单位分为若干个小链表，再将小链表进行翻转，最后将小链表链接起来，依次进行，当小链表的长度小于k时，将其直接连接在链表后面即可。

部分代码图示：



代码实现：

#include
#include
#include

typedef int DataType;

typedef struct ListNode
{
DataType _data;
struct ListNode* _next;
}Node,*pNode,*pList;

void Init(pList* pplist)
{
assert(pplist);
*pplist = NULL;
}

pNode BuyNode(DataType x)
{
pNode pnode = (pNode)malloc(sizeof(Node));
if (pnode == NULL)
{
perror("malloc");
return NULL;
}
pnode->_data = x;
pnode->_next = NULL;
return pnode;
}

void Push(pList* pplist,DataType x)
{
pNode NewNode = BuyNode(x);
if (*pplist == NULL)
{
*pplist = NewNode;
}
else
{
pNode cur = *pplist;
while (cur->_next)
{
cur = cur->_next;
}
cur->_next = NewNode;
}
}

pNode Reverse(pList plist)
{
pNode cur = plist;
if(cur == NULL)
return NULL;
if (cur->_next)
{
Reverse(cur->_next);
}
printf("%d ", cur->_data);
return cur;
}

pNode getLastNode(pList plist)
{
pNode pHead = plist;
while (pHead->_next != NULL)
{
pHead = pHead->_next;
}
return pHead;

}

pNode SwapListByK(pList plist, size_t k)
{
pNode pnode = plist;
pNode pNewNode;
pNode pNextNode;
pNode LastNode = NULL;
pNode tmp = NULL;
size_t pos;
if (k <= 1)
return plist;

plist = NULL;
while (pnode)
{
pos = 0;
pNewNode = pnode;
while (pnode && pos < k - 1)
{
tmp = pNewNode;
pnode = pnode->_next;
if (pnode == NULL)
{
break;
}
pos++;
}
if (pnode == NULL)
{
return tmp;        //如果需要反转的不足k个元素，则直接连在后面
}
if (pnode)
{
pNextNode = pnode->_next;
pnode->_next = NULL;
if (LastNode != NULL)
{
LastNode->_next = NULL;
}
pNewNode = Reverse(pNewNode);
if (plist == NULL)
plist = pNewNode;
else
LastNode->_next = pNewNode;

pnode = getLastNode(pNewNode);
pnode->_next = pNextNode;
LastNode = pnode;
pnode = pNextNode;
}
else
{
break;
}
}
return pnode;
}

void Printf(pList plist)
{
pList cur = plist;
while (cur)
{
printf("%d ", cur->_data);
cur = cur->_next;
}
printf(" NULL\n");
}

void Test()
{
pList plist;
Init(&plist);
Push(&plist, 1);
Push(&plist, 2);
Push(&plist, 3);
Push(&plist, 4);
Push(&plist, 5);
Push(&plist, 6);
Push(&plist, 7);
Printf(plist);

pNode ret = SwapListByK(plist, 3);
Printf(ret);

}

测试结果：