Sword refers to offer 22, the kth node from the bottom in the linked list

• analysis

      Double pointer, let one pointer go n steps first, then the fast pointer and slow pointer move backward at the same time, until the fast pointer moves to the end of the linked list.

• Code

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* getKthFromEnd(ListNode* head, int k) {
        ListNode* fast = head;
        while(k > 0 && fast != nullptr){
            fast = fast -> next;
            k--;
        }

        ListNode* slow = head;

        while(fast != nullptr){
            fast = fast -> next;
            slow = slow -> next;
        }

        return slow;
    }
};