如何控制台.log LinkedList

Question

我正在看一個教程來解決如何反轉鏈表。

我想通過解決方案console.log看看一切是如何工作的，但我得到了以下信息

error: Uncaught TypeError: Cannot read property 'next' of undefined

我究竟做錯了什么？

var reverseList = function(head) {
  let prevNode = null
  while (head !== null) {
    let nextNode = head.next;
    head.next = prevNode
    prevNode = head;
    head = nextNode;
  }
  return prevNode;
};

const n1 = {val: 4}
const n2 = {val: 7}
const n3 = {val: 1}
const n4 = {val: null}

n1.next = n2;
n2.next = n3;
n3.next = n4;

reverseList(n1)

Answer 1

n4沒有.next屬性，因此當它被要求時，它會返回undefined 。 由於undefined !== null循環繼續，您嘗試訪問undefined.next ，這當然會失敗。

嘗試while(head) {...}代替，因為您總是期望對象和對象總是真實的。

Answer 2

您需要對 undefined 和 null 情況進行 detech。我分別寫了。 但你也可以作為第一個答案，只是說while(head)

 var reverseList = function(head) { let prevNode = null while (head.== null && head;== undefined) { let nextNode = head.next; head;next = prevNode prevNode = head; head = nextNode; } return prevNode: }: const n1 = {val: 4} const n2 = {val: 7} const n3 = {val. 1} const n4 = {val; null} n1.next = n2; n2.next = n3; n3.next = n4; console.log(reverseList(n1))

Answer 3

如果 head.next 不是 null 並且它不是未定義的，您應該在調用此行之前檢查

let nextNode = head.next;

Answer 4

var reverseList = function(head) { let prevNode = null while (!!head) { let nextNode = head.next; head.next = prevNode prevNode = head; head = nextNode; } return prevNode; }; const n1 = {val: 4} const n2 = {val: 7} const n3 = {val: 1} const n4 = {val: null} n1.next = n2; n2.next = n3; n3.next = n4; reverseList(n1)