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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:
[0, 100]
.0 <= Node.val <= 100
ListNode* swapPairs(ListNode* head) {
if(!head || !head->next) return head; //If there are less than 2 nodes in the given nodes, then no need to do anything just return the list as it is.
ListNode* dummyNode = new ListNode();
ListNode* prevNode=dummyNode;
ListNode* currNode=head;
while(currNode && currNode->next){
prevNode->next = currNode->next;
currNode->next = prevNode->next->next;
prevNode->next->next = currNode;
prevNode = currNode;
currNode = currNode->next;
}
return dummyNode->next;
}
public class Solution {
public ListNode swapPairs(ListNode head) {
if ((head == null)||(head.next == null))
return head;
ListNode n = head.next;
head.next = swapPairs(head.next.next);
n.next = head;
return n;
}
}
class Solution(object):
def swapPairs(self, head):
if not head or not head.next: return head
dummy = ListNode(0)
dummy.next = head
cur = dummy
while cur.next and cur.next.next:
first = cur.next
sec = cur.next.next
cur.next = sec
first.next = sec.next
sec.next = first
cur = cur.next.next
return dummy.next
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