输入一个链表，输出该链表中倒数第k个结点。
/* struct ListNode { int val; struct ListNode *next; ListNode(int x) : val(x), next(NULL) { } };*/ class Solution { public: ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) { //快慢指针，转化为正数第几个 unsigned int temp = k; ListNode* fast = pListHead; if (temp == 0) return nullptr; //先走到正数第K+1个 while (temp--) { if (fast) fast = fast->next; else return nullptr; } //快指针走到尾，慢指针就走到了倒数第K个 ListNode* slow = pListHead; while (fast) { fast = fast->next; slow = slow->next; } return slow; } };