代码随想录算法训练营第四天 | 24. 两两交换链表中的节点 19. 删除链表的倒数第 N 个结点

24. 两两交换链表中的节点

19. 删除链表的倒数第 N 个结点

双指针

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
var removeNthFromEnd = function(head, n) {
    let dummy = new ListNode(null, head);

    let fast = dummy;
    let slow = dummy;

    while(fast && n > 0) {
        fast = fast.next;
        n--;
    }
    // 多走一步，为了让slow指在要删除的节点的前一个位置
    fast = fast.next;

    while(fast) {
        slow = slow.next;
        fast = fast.next;
    }

    let next = slow.next;
    slow.next = next.next;

    return dummy.next;
};