剑指 Offer 22. 链表中倒数第k个节点

方法一 双指针

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var getKthFromEnd = function(head, k) {
    //双指针，第一个指针先走k步
    let slow = head, fast = head;
    while(k && fast) {
        k--;
        fast = fast.next;
    }
    while(fast) {
        slow = slow.next;
        fast = fast.next;
    }
    return slow;
};

 

方法二 数组

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var getKthFromEnd = function(head, k) {
    let res = [];
    while(head) {
        res.push(head);
        head = head.next;
    }
    return res[res.length - k];
};