检查链接列表是否成对排序

给定一个链表。任务是检查链接列表是否成对排序。

如果每对连续的数字对都按排序(非降序)顺序，则认为链表是成对排序的。如果节点数为奇数，则忽略最后一个节点，并且结果基于剩余的偶数个节点。

例子：

Input: List =  10 -> 15 -> 9 -> 9 -> 1 -> 5
Output: YES

Input: List = 10 -> 15 -> 8 -> 9 -> 10 -> 5
Output: NO

方法：想法是从左到右遍历链表。成对比较节点，如果任何一对违反属性，则返回false。如果没有一对违反属性，则返回True。

下面是上述方法的实现：

C++

// C++ program to check if linked list is
// pairwise sorted
#include 
  
using namespace std;
  
// A linked list node
struct Node {
    int data;
    struct Node* next;
};
  
// Function to check if linked list is
// pairwise sorted
bool isPairWiseSorted(struct Node* head)
{
    bool flag = true;
  
    struct Node* temp = head;
  
    // Traverse further only if there
    // are at-least two nodes left
    while (temp != NULL && temp->next != NULL) {
        if (temp->data > temp->next->data) {
            flag = false;
            break;
        }
  
        temp = temp->next->next;
    }
  
    return flag;
}
  
// Function to add a node at the
// beginning of Linked List
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
  
    /* put in the data */
    new_node->data = new_data;
  
    /* link the old list off the new node */
    new_node->next = (*head_ref);
  
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
  
// Driver program to test above function
int main()
{
    struct Node* start = NULL;
  
    /* The constructed linked list is: 
    10->15->9->9->1->5 */
    push(&start, 5);
    push(&start, 1);
    push(&start, 9);
    push(&start, 9);
    push(&start, 15);
    push(&start, 10);
  
    if (isPairWiseSorted(start))
        cout << "YES";
    else
        cout << "NO";
  
    return 0;
}

Java

// Java program to check if linked list is 
// pairwise sorted 
class GFG
{ 
  
// A linked list node 
static class Node
{ 
    int data; 
    Node next; 
}; 
static Node start;
  
// Function to check if linked list is 
// pairwise sorted 
static boolean isPairWiseSorted(Node head) 
{ 
    boolean flag = true; 
  
    Node temp = head; 
  
    // Traverse further only if there 
    // are at-least two nodes left 
    while (temp != null && temp.next != null) 
    { 
        if (temp.data > temp.next.data) 
        { 
            flag = false; 
            break; 
        } 
  
        temp = temp.next.next; 
    } 
    return flag; 
} 
  
// Function to add a node at the 
// beginning of Linked List 
static void push(Node head_ref, int new_data) 
{ 
      
    /* allocate node */
    Node new_node = new Node(); 
  
    /* put in the data */
    new_node.data = new_data; 
  
    /* link the old list off the new node */
    new_node.next = head_ref; 
  
    /* move the head to point to the new node */
    head_ref = new_node; 
        start = head_ref;
} 
  
// Driver Code
public static void main(String[] args) 
{
    start = null; 
  
    /* The constructed linked list is: 
    10.15.9.9.1.5 */
    push(start, 5); 
    push(start, 1); 
    push(start, 9); 
    push(start, 9); 
    push(start, 15); 
    push(start, 10); 
  
    if (isPairWiseSorted(start)) 
        System.out.println("YES");
    else
        System.out.println("NO");
    }
}
  
// This code is contributed by PrinciRaj1992

Python

# Python program to check if linked list is 
# pairwise sorted 
  
# Linked List node 
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
          
start = None
  
# Function to check if linked list is 
# pairwise sorted 
def isPairWiseSorted(head) :
  
    flag = True
  
    temp = head 
  
    # Traverse further only if there 
    # are at-least two nodes left 
    while (temp != None and temp.next != None) :
      
        if (temp.data > temp.next.data) :
            flag = False
            break
          
        temp = temp.next.next
      
    return flag 
  
# Function to add a node at the 
# beginning of Linked List 
def push(head_ref, new_data) :
  
    global start
    # allocate node 
    new_node = Node(0) 
  
    # put in the data 
    new_node.data = new_data 
  
    # link the old list off the new node 
    new_node.next = head_ref 
  
    # move the head to point to the new node 
    head_ref = new_node 
    start = head_ref
  
# Driver Code
start = None
  
# The constructed linked list is: 
# 10.15.9.9.1.5 
push(start, 5) 
push(start, 1) 
push(start, 9) 
push(start, 9) 
push(start, 15) 
push(start, 10) 
  
if (isPairWiseSorted(start)) :
    print("YES")
else:
    print("NO")
      
# This code is contributed by Arnab Kundu

C#

// C# program to check if linked list is 
// pairwise sorted 
using System;
class GFG
{ 
  
// A linked list node 
public class Node
{ 
    public int data; 
    public Node next; 
}; 
static Node start;
  
// Function to check if linked list is 
// pairwise sorted 
static Boolean isPairWiseSorted(Node head) 
{ 
    Boolean flag = true; 
  
    Node temp = head; 
  
    // Traverse further only if there 
    // are at-least two nodes left 
    while (temp != null && temp.next != null) 
    { 
        if (temp.data > temp.next.data) 
        { 
            flag = false; 
            break; 
        } 
  
        temp = temp.next.next; 
    } 
    return flag; 
} 
  
// Function to add a node at the 
// beginning of Linked List 
static void push(Node head_ref, int new_data) 
{ 
      
    /* allocate node */
    Node new_node = new Node(); 
  
    /* put in the data */
    new_node.data = new_data; 
  
    /* link the old list off the new node */
    new_node.next = head_ref; 
  
    /* move the head to point to the new node */
    head_ref = new_node; 
    start = head_ref;
} 
  
// Driver Code
public static void Main(String[] args) 
{
    start = null; 
  
    /* The constructed linked list is: 
    10.15.9.9.1.5 */
    push(start, 5); 
    push(start, 1); 
    push(start, 9); 
    push(start, 9); 
    push(start, 15); 
    push(start, 10); 
  
    if (isPairWiseSorted(start)) 
        Console.WriteLine("YES");
    else
        Console.WriteLine("NO");
    }
}
  
// This code is contributed by Rajput-Jiv

输出：

YES