C程序删除右侧具有较大值的节点

给定一个单链表，删除右边所有值较大的节点。

例子：

Input: 12->15->10->11->5->6->2->3->NULL
Output: 15->11->6->3->NULL
Explanation: 12, 10, 5 and 2 have been deleted because there is a 
             greater value on the right side. When we examine 12, 
             we see that after 12 there is one node with a value 
             greater than 12 (i.e. 15), so we delete 12. When we 
             examine 15, we find no node after 15 that has a value 
             greater than 15, so we keep this node. When we go like 
             this, we get 15->6->3

Input: 10->20->30->40->50->60->NULL
Output: 60->NULL
Explanation: 10, 20, 30, 40, and 50 have been deleted because 
             they all have a greater value on the right side.

Input: 60->50->40->30->20->10->NULL
Output: No Change.

方法1（简单）：
使用两个循环。在外循环中，一个一个地挑选链表的节点。在内部循环中，检查是否存在值大于选取的节点的节点。如果存在值较大的节点，则删除选取的节点。
时间复杂度： O(n^2)

方法2（使用反向）：
感谢 Paras 提供以下算法。
1. 颠倒列表。
2. 遍历反向列表。保持最大值到现在。如果下一个节点小于max，则删除下一个节点，否则max =下一个节点。
3. 再次反转列表以保留原始顺序。
时间复杂度： O(n)
感谢 R.Srinivasan 提供以下代码。

C

// C program to delete nodes which have
// a greater value on right side
#include 
#include 
 
// Structure of a linked list
// node
struct Node
{
    int data;
    struct Node* next;
};
 
// Prototype for utility functions
void reverseList(struct Node** headref);
void _delLesserNodes(struct Node* head);
 
/* Deletes nodes which have a node with
   greater value node on left side */
void delLesserNodes(struct Node** head_ref)
{
    // 1. Reverse the linked list
    reverseList(head_ref);
 
    /* 2. In the reversed list, delete nodes
          which have a node with greater value
          node on left side. Note that head node
          is never deleted because it is the leftmost
          node.*/
    _delLesserNodes(*head_ref);
 
    /* 3. Reverse the linked list again to retain the
          original order */
    reverseList(head_ref);
}
 
/* Deletes nodes which have greater value
   node(s) on left side */
void _delLesserNodes(struct Node* head)
{
    struct Node* current = head;
 
    // Initialize max
    struct Node* maxnode = head;
    struct Node* temp;
 
    while (current != NULL &&
           current->next != NULL)
    {
        /* If current is smaller than max,
           then delete current */
        if (current->next->data <
            maxnode->data)
        {
            temp = current->next;
            current->next = temp->next;
            free(temp);
        }
 
        /* If current is greater than max,
           then update max and move current */
        else
        {
            current = current->next;
            maxnode = current;
        }
    }
}
 
/* Utility function to insert a
   node at the beginning */
void push(struct Node** head_ref,
          int new_data)
{
    struct Node* new_node =
           (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = *head_ref;
    *head_ref = new_node;
}
 
/* Utility function to reverse a
   linked list */
void reverseList(struct Node** headref)
{
    struct Node* current = *headref;
    struct Node* prev = NULL;
    struct Node* next;
    while (current != NULL)
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    *headref = prev;
}
 
/* Utility function to print a
   linked list */
void printList(struct Node* head)
{
    while (head != NULL)
    {
        printf("%d ", head->data);
        head = head->next;
    }
    printf("");
}
 
// Driver code
int main()
{
    struct Node* head = NULL;
 
    /* Create following linked list
       12->15->10->11->5->6->2->3 */
    push(&head, 3);
    push(&head, 2);
    push(&head, 6);
    push(&head, 5);
    push(&head, 11);
    push(&head, 10);
    push(&head, 15);
    push(&head, 12);
 
    printf("Given Linked List ");
    printList(head);
 
    delLesserNodes(&head);
 
    printf("Modified Linked List ");
    printList(head);
 
    return 0;
}

输出：

Given Linked List 
12 15 10 11 5 6 2 3
Modified Linked List 
15 11 6 3

时间复杂度：O(n)

辅助空间：O(1)

资料来源：https://www.geeksforgeeks.org/forum/topic/amazon-interview-question-for-software-engineerdeveloper-about-linked-lists-6

详情请参考右侧有更大价值的删除节点的完整文章！