面试常考的链表操作

1、链表的结构

typedef int Data; 
struct ListNode {
     Date data;
     ListNode *pNext;
};

2、链表的逆序

ListNode *reverseList(ListNode *pHead)
{
     ListNode *pReversedHead = NULL;
     ListNode *pNode = pHead;
     ListNode *pPrev = NULL;
 
     while (pNode != NULL) {
         ListNode *pNext = pNode->pNext;
         if (pNext == NULL) 
             pReversedHead = pNode;
  
         pNode->pNext = pPrev;
         pPrev = pNode;
         pNode = pNext; 
     }
     return pReversedHead; 
}

3、找出倒数第k个

ListNode* findKthToTail(ListNode* pListHead, unsigned int k)
{
     if (pListHead == NULL || k == 0)
          return NULL;
  
     ListNode *pAhead = pListHead;
     ListNode *pBehind = NULL;
 
     for (unsigned int i = 0; i < k - 1; i++) {
          if (pAhead->pNext != NULL)
               pAhead = pAhead->pNext;
          else 
               return NULL;
     }
 
     pBehind = pListHead;
     while (pAhead->pNext != NULL) {
          pAhead = pAhead->pNext;
          pBehind = pBehind->pNext
     }
     return pBehind;
}

4、找出中间元素

 ListNode *getMiddleNode(ListNode *pNode)
{
     ListNode *firstNode = pNode;
     ListNode *backNode = pNode;
 
     while (firstNode != NULL) {
          firstNode = firstNode->pNext->pNext;
          backNode = backNode->pNext;
     }
     return backNode;
}

5、判断链表是否有环

 bool judgeListCricle(ListNode *pNode)
{
     if (pNode == NULL)
          return false;
 
     ListNode *first = pNode;
     ListNode *back = pNode;
 
     while(firt->pNext!=NULL && back->pNext->pNext!=NULL) {
          first = first->pNext;
          back = back->pNext->pNext;
          if (first == back)
               return ture;
     }
     return false;
}