题目

https://leetcode-cn.com/problems/reverse-linked-list/

解题

  1. /**
  2.  * Definition for singly-linked list.
  3.  * function ListNode(val, next) {
  4.  *     this.val = (val===undefined ? 0 : val)
  5.  *     this.next = (next===undefined ? null : next)
  6.  * }
  7.  */
  8. /**
  9.  * @param {ListNode} head
  10.  * @return {ListNode}
  11.  */
  12. var reverseList = function(head) {
  13.     if (head === null) {
  14.         return null
  15.     }
  16.     // 第一种、迭代
  17.     // const stack = []
  18.     // let current = head
  19.     // while(current) {
  20.     //     stack.push(current.val)
  21.     //     current = current.next
  22.     // }
  23.     // for (let i = stack.length - 1; i >= 0; i--) {
  25.     //     if (i === stack.length - 1) {
  26.     //         head = current = new ListNode(stack[i])
  27.     //     } else {
  28.     //         current.next = new ListNode(stack[i])
  29.     //         current = current.next
  30.     //     }
  31.     // }
  32.     // return head
  34.     // 第二种 、递归
  36.     const recursion = (node) => {
  37.         if (node.next === null) {
  38.             head = node
  39.             return node
  40.         }
  42.         const prev = recursion(node.next)
  43.         prev.next = new ListNode(node.val)
  44.         return prev.next
  45.     }
  47.     recursion(head)
  48.     return head
  51. };