Node Swap

• Time : O(n)
• Space : O(1)

using namespace std;

// This is an input struct. Do not edit.
class LinkedList {
public:
    int value;
    LinkedList *next = nullptr;

    LinkedList(int value) { this->value = value; }
};

LinkedList *nodeSwap(LinkedList *head) {
		if(head == nullptr) return nullptr;
    LinkedList *dummy = new LinkedList(-1);
    dummy->next = head;
    LinkedList *prv = dummy, *now = head, *nxt;
    while(now) {
        if(now->next == nullptr) break;
        nxt = now->next;
        LinkedList* tmp = nxt->next;
        prv->next = nxt;
        nxt->next = now;
        now->next = tmp;
        
        prv = now;
        now = tmp;
    }
    return dummy->next;
}