24. Swap Nodes in Pairs
1. Description
Given a linked list, swap every two adjacent nodes and return its head.
You may not modify the values in the list’s nodes. Only nodes itself may be changed.
2. Example
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]
3. Constraints
- The number of nodes in the list is in the range [0, 100].
- 0 <= Node.val <= 100
4. Solutions
My Accepted Solution
n is the sum of nodes in m_head
Time complexity: O(n)
Space complexity: O(1)
class Solution
{
public:
// ListNode* swapPairs(ListNode* head)
ListNode* swapPairs(ListNode *m_head)
{
if(!m_head || !m_head->next) return m_head;
auto result = new ListNode();
result->next = m_head;
for(auto iter = result, firstNode = m_head, secondNode = m_head->next; firstNode && firstNode->next; )
{
firstNode->next = secondNode->next;
secondNode->next = firstNode;
iter->next = secondNode;
iter = firstNode;
firstNode = firstNode->next;
secondNode = (firstNode ? firstNode->next : nullptr);
}
return result->next;
}
};