Sword finger offer 22 The penultimate node in the linked list

Original link ： The finger of the sword Offer 22. Last in the list k Nodes

 solution:
        Speed pointer , Let's go first k Step , Then the pointer moves forward quickly and slowly , When the fast pointer reaches the end , The slow pointer is the penultimate k individual .

class Solution {
public:
    ListNode* getKthFromEnd(ListNode* head, int k) {
        ListNode *fast = head;
        ListNode *slow = head;
        while(fast != NULL && k) {
            fast = fast->next;
            k--;
        }

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