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class Solution {
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 public:
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  // Recursive Approach
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  ListNode *deleteDuplicates(ListNode *head) {
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    // base case
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    if (head == NULL || head->next == NULL) return head;
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    // 1-1-2-3-3
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    // we are giving next pointer to recursion and telling it to get it done for
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    // me
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    ListNode *newNode = deleteDuplicates(head->next); // 1-2-3-3
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    // after recursion we will get-- 1-2-3
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    // now we will compare the head node with the newNode
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    //  if both are same then return the newNode
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    // else return the current head
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    if (head->val == newNode->val)
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      return newNode;
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    else {
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      head->next = newNode;
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      return head;
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    }
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  }
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};
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class Solution {
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 public:
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  // Iterative Approach
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  ListNode *deleteDuplicates(ListNode *head) {
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    if (head == NULL || head->next == NULL) return head;
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    ListNode *temp = head;
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    while (temp->next != NULL) {
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      // if the 2 consecutive nodes are equal then just delete the in between
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      if (temp->val == temp->next->val) {
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        temp->next = temp->next->next;
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        // dont need to update the temp variable as there can be more than 2
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        // duplicates
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        //  1-1-1-1-2-3-4-4-NULL
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      } else {
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        temp = temp->next; // update the temp variable
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      }
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    }
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    return head;
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  }
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};