Swap Nodes in Pairs

06/25/2016 Linked List

Question

Given a linked list, swap every two adjacent nodes and return its head. For example, Given 1->2->3->4, you should return the list as 2->1->4->3. Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

Solution

Result: Accepted Time: 0ms

Here should be some explanations.

struct ListNode* swapPairs(struct ListNode* head) {
    struct ListNode Head;
    struct ListNode * before,* now,* after;
    Head.next = head;
    before = &Head;
    now = head;
    if( head == NULL)
        return head;
    after = head->next;
    while(after != NULL)
    {
        before->next = after;
        now->next = after->next;
        after->next = now;

        before = now;
        now = now->next;
        if(now == NULL)
            break;
        after = now->next;
    }
    return Head.next;
}

Complexity Analytics

  • Time Complexity:
  • Space Complexity: