• 先让fast领先k步。倒数第k节点 - 图1

    • 逐步向后移动

      1.   class ListNode {
      2.       val: number;
      3.       next: ListNode | null;
      4.       constructor(val?: number, next?: ListNode | null) {
      5.           this.val = val === undefined ? 0 : val;
      6.           this.next = next === undefined ? null : next;
      7.       }
      8.   }
      9.   function getKthFromEnd(head: ListNode | null, k: number): ListNode | null {
      10.       let slow = head;
      11.       let fast = head;
      12.       // fast - slow = k
      13.       for (let i = 0; i < k; i++) {
      14.           if (fast === null) {
      15.               return null;
      16.           }
      17.           fast = fast.next;
      18.       }
      19.       while (fast) {
      20.           slow = slow!.next;
      21.           fast = fast.next;
      22.       }
      24.       return slow;
      25.   }