How PHP gets the bottom-count K-nodes in a linked list

This article mainly introduces the method of PHP to get the countdown K node in the chain list, involving PHP's traversal, judgment and other related operation skills, the friend who is interested in PHP can refer to this article

Problem

Enter a list to output the last K nodes in the linked list.

Solution Ideas

Note that this topic is the return node, not the return value. The return value can be stored with a stack. The return node cannot do so.

Set two pointers so that the first pointer moves k-1 times. Then the two pointers move at the same time, and when the first pointer reaches the last node, the second pointer is at the bottom of the K-node.

Note the boundary: the K length may exceed the list length, so when the first pointer's next is empty, NULL is returned

Implementation code

<?php/*class listnode{var $val; var $next = NULL, function construct ($x) {  $this->val = $x;}} */function Findkthtotail ($head, $k) {if ($head = = NULL | | $k ==0)  return NULL; $pre = $head; $last = $head; for ($i = 1; $ i< $k; $i + +) {  if ($last->next = = null)   return null;  else   $last = $last->next;} while ($last->next! = NULL) {  $pre = $pre->next;  $last = $last->next; } return $pre;}

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