Interview ---- K elements at the bottom of the linked list

Although this question is simple, you must be careful. The bug-free capability is very important.

Analysis: if you do not know the length of the linked list, you can use the double pointer method to let a pointer go k steps first, and then the two pointers go at the same time,

When the previous pointer becomes NULL, the first pointer is the last k node ..

However, consider k <0, k> length and so on ..

Another typical example of double pointer is to find whether the two linked list intersection, see the http://blog.csdn.net/shoulinjun/article/details/20127223

// copyright @ L.J.SHOU Mar.05, 2014// find the last kth node in a list#include 
 
  #include 
  
   using namespace std;struct ListNode{  int val;  ListNode *next;  ListNode(int x):val(x), next(NULL){}};ListNode* LastKthNode(ListNode *list, int k){  assert(k >= 0);  if(k == 0 || list == NULL)    return NULL;  ListNode *p(list);  for(; k>0 && p; --k)p = p->next;  if(k > 0) // list length less than k    return NULL;  while(p)  {    p = p->next;list = list->next;  }    return list;}int main(void){  ListNode *list(NULL), *node(NULL);  list = new ListNode(1);  list->next = new ListNode(2);  list->next->next = new ListNode(3);  node = LastKthNode(list, 30);  if(node != NULL)    cout << "node is : " << node->val << endl;  while(list){    node = list->next;delete list;list = node;  }  return 0;}