Leetcode 24 Swap Nodes in Pairs Solution in java | Hindi Coding Community

 

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]

public class Solution {
  public ListNode swapPairs(ListNode head) {
    if(head==null || head.next==null) return head;
    ListNode newHead = head.next, a=head,b=a.next,pre = null;
    while(a!=null && b!=null){
      a.next = b.next;
      b.next = a;
      if(pre!=null) pre.next = b;
      if(a.next==null) break;
      b = a.next.next;
      pre = a;
      a = a.next;
    }
    return newHead;
  }
}