排序雙向鏈表（Java空指針）的問題

Question

我正試圖解決hackerrank上的問題。要解決的問題是：

「給出指向已排序的雙向鏈表的頭節點的指針和要插入列表的整數。創建一個節點並將其插入列表中的適當位置。頭節點可能爲NULL，表示列表爲空。「

他們提供的節點類定義爲

/* 
Insert Node at the end of a linked list 
head pointer input could be NULL as well for empty list 
Node is defined as 

class Node { 
    int data; 
    Node next; 
    Node prev; 
} 
*/ 

我嘗試的解決方案是

Node SortedInsert(Node head,int data) 
{ 
    // new node to insert into linked list 
    Node newNode = new Node(); 
    newNode.data = data; 

    if (head == null) 
    { 
     return newNode; 
    } 

    else 
    { 
     // start at beginning of list 
     Node cur = head; 

     // traverse through sorted list 
     while (cur != null && cur.next != null) 
     {   
      if (data < cur.next.data) 
      { 
       newNode.next = cur.next; 
       newNode.prev = cur; 
       cur.next.prev = newNode; 
       cur.next = newNode; 

       return head; 
      } 

      else 
      { 
       cur = cur.next; 
      } 
     } 

     return head; 
    } 
} 

我不太知道什麼是錯在這裏，但hackerrank是說我的解決方案是不正確。有什麼想法可能會出錯？

Answer 1

假設我們的DLL是1 = 2 = 3 = 4 = 5

現在考慮的情況：加6〜DLL 循環將不會覆蓋邊界情形。

while (cur != null && cur.next != null) 
    {   
     if (data < cur.next.data) 
     { 
      newNode.next = cur.next; 
      newNode.prev = cur; 
      cur.next.prev = newNode; 
      cur.next = newNode; 

      return head; 
     } 

     else 
     { 
      cur = cur.next; 
     } 
    } 

修改：

if(data < cur.data) { 
      newNode.next = cur; 
      newNode.prev = null; 
      cur.prev = newNode; 

      head = newNode; 
      return head; 
    } 

    while (cur != null) 
    {   
     if (data >= cur.data) 
     { 
      if(cur.next == null) { 
       newNode.next = cur.next; 
       newNode.prev = cur; 
       cur.next = newNode; 

       return head;  
      } 

      newNode.next = cur.next; 
      newNode.prev = cur; 
      cur.next.prev = newNode; 
      cur.next = newNode; 

      return head; 
     } 

     else 
     { 
      cur = cur.next; 
     } 
    }