【牛客網】鏈表中倒數第k個結點

• 題目：
  輸入一個鏈表，輸出該鏈表中倒數第k個結點。

• AC的代碼：

class Solution {
public:
    ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
           if(pListHead==NULL)return NULL;
           int sum=1,sum1=1;
           ListNode *Node=pListHead;
           while(Node->next!=NULL){
               sum+=1;
               Node=Node->next;
           }
           if(k==1)return Node;//如果是最後一個節點
           Node=pListHead;
           while(Node->next!=NULL){
               if(sum1==sum-k+1)return Node;
               Node=Node->next;
               sum1+=1;
           }//如果是其他節點
           return NULL;
     }
};

• 劍指Offer上的代碼

class Solution {
public:
    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->next!=NULL)
            pAhead = pAhead->next;
        else return NULL;
      }
     pBehind = pListHead;
     while (pAhead->next != NULL){
        pAhead = pAhead->next;
        pBehind = pBehind->next;
     }
     return pBehind;
     }//只需遍歷一遍
};