Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)
Test Cases
Example 1:
Input: head = [1,2,3,4]
Output: [2,1,4,3]
Explanation:
1->2->3->4 -> 2->1->4->3
Example 2:
Input: head = []
Output: []
Solution
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* swapPairs(struct ListNode* head){
if (head == NULL || head->next == NULL) return head;
struct ListNode *l1 = head, *l2 = head->next;
l1->next = l2->next;
l2->next = l1;
l1->next = swapPairs(l1->next);
return l2;
}/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if (head == NULL || head->next == NULL) return head;
ListNode *l1 = head, *l2 = head->next;
l1->next = l2->next;
l2->next = l1;
l1->next = swapPairs(l1->next);
return l2;
}
};package swap_nodes_in_pairs
type ListNode struct {
Val int
Next *ListNode
}
func swapPairs(head *ListNode) *ListNode {
if head == nil || head.Next == nil {
return head
}
l1 := head
l2 := head.Next
l1.Next = l2.Next
l2.Next = l1
l1.Next = swapPairs(l1.Next)
return l2
}/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode swapPairs(ListNode head) {
if (head == null || head.next == null) return head;
ListNode l1 = head, l2 = head.next;
l1.next = l2.next;
l2.next = l1;
l1.next = swapPairs(l1.next);
return l2;
}
}from typing import Optional
# Definition for singly-linked list.
class ListNode:
def __init__(self, val=0, next=None):
self.val = val
self.next = next
class Solution:
def swapPairs(self, head: Optional[ListNode]) -> Optional[ListNode]:
if not head or not head.next:
return head
l1, l2 = head, head.next
l1.next = l2.next
l2.next = l1
l1.next = self.swapPairs(l1.next)
return l2