Algorithm
Problem Name: 24. Swap Nodes in Pairs
Problem Link: https://leetcode.com/problems/swap-nodes-in-pairs/
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.)
Example 1:
Input: head = [1,2,3,4] Output: [2,1,4,3]
Example 2:
Input: head = [] Output: []
Example 3:
Input: head = [1] Output: [1]
Constraints:
- The number of nodes in the list is in the range
[0, 100]. 0 <= Node.val <= 100
Code Examples
#1 Code Example with C Programming
Code -
C Programming
struct ListNode* swapPairs(struct ListNode* head) {
struct ListNode *a, *b, *c;
a = head;
if (a && a->next) {
b = a->next;
c = b->next;
b->next = a;
a->next = swapPairs(c);
return b;
}
return a;
}
Input
Output
#2 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if (!head || !head->next) return head;
ListNode res(0);
ListNode *pre = &res, *one = head, *two = head->next;
while (one && two) {
one->next = two->next;
two->next = one;
pre->next = two;
pre = one;
one = one->next;
if (one) two = one->next;
}
return res.next;
}
};
Input
Output
#3 Code Example with Java Programming
Code -
Java Programming
class Solution {
public ListNode swapPairs(ListNode head) {
ListNode curr = head;
ListNode prev = null;
while (curr != null && curr.next != null) {
ListNode nextNode = curr.next;
if (curr == head) {
head = nextNode;
}
curr.next = nextNode.next;
nextNode.next = curr;
if (prev != null) {
prev.next = nextNode;
}
prev = curr;
curr = curr.next;
}
return head;
}
}
Input
Output
#4 Code Example with Javascript Programming
Code -
Javascript Programming
const swapPairs = function(node) {
const head = new ListNode(-1);
let cur = head;
while (node !== null) {
if (node.next !== null) {
let one = node;
let two = node.next;
let three = node.next.next;
cur.next = two;
two.next = one;
one.next = three;
cur = cur.next.next;
node = three;
} else {
cur.next = node;
break;
}
}
return head.next;
};
Input
Output
#5 Code Example with Python Programming
Code -
Python Programming
class Solution:
def swapPairs(self, head: ListNode) -> ListNode:
if not head or not head.next: return head
first = head.next
second = head
second.next = self.swapPairs(first.next)
first.next = second
return first
Input
Output
#6 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _024_SwapNodesInPairs
{
public ListNode SwapPairs(ListNode head)
{
var dummyHead = new ListNode(-1);
dummyHead.next = head;
ListNode p = dummyHead, q;
while (p.next != null && p.next.next != null)
{
q = p.next;
p.next = q.next;
q.next = p.next.next;
p.next.next = q;
p = q;
}
return dummyHead.next;
}
}
}
Input
Output