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//Approach-2 (Using only One Pass)
class Solution {
public:
    ListNode* swapNodes(ListNode* head, int k) {
        ListNode* p1 = NULL;
        ListNode* p2 = NULL;
        
        ListNode* temp = head;
        
        while(temp) {
            
            if(p2 != NULL)
                p2 = p2->next;
                
            
            k--;
            if(k == 0) {
                p1 = temp;
                p2 = head;
            }
            
            
            temp = temp->next;
            
        }
        
        swap(p1->val, p2->val);
        return head;
    }
};