[The sword refers to the offer brushing the question] Acwing 33. The kth node from the bottom in the linked list

Question type: double pointer

The idea is that the two pointers are separated by k. When the latter pointer reaches the end, the previous pointer is the correct answer.

topic

Input a linked list, output the k-th penultimate in the linked list

a node.

Notice:

k >= 1;
如果 k

大于链表长度，则返回 NULL;

Sample

Input: linked list: 1->2->3->4->5, k=2

output: 4

java code

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    
    
    public ListNode findKthToTail(ListNode pListHead, int k) {
    
    
        if (pListHead == null) return null;
        ListNode pre = pListHead;
        ListNode last = pListHead;
        for (int i = 1; i < k; i++) {
    
    
            if (last.next == null) return null;
            last = last.next;
        }
        
        while (last.next != null) {
    
    
            last = last.next;
            pre = pre.next;
        }
        
        return pre;
    }
}