剑指 Offer 22. 链表中倒数第k个节点

快慢指针。

/**
 * 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) {
        if(head == nullptr || k == 0) return nullptr;
        
        ListNode *fast = head, *slow = head;
        for (int i = 0; i < k - 1; i++) {
            if (fast->next == nullptr)
                return nullptr;
            else 
                fast = fast->next;
        }

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

        return slow;
    }
};