203. Remove Linked List Elements

 203. Remove Linked List Elements


Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

 

Example 1:

Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]

Example 2:

Input: head = [], val = 1
Output: []

Example 3:

Input: head = [7,7,7,7], val = 7
Output: []

 

Constraints:

  • The number of nodes in the list is in the range [0, 104].
  • 1 <= Node.val <= 50
  • 0 <= val <= 50

Solution in C++


/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* headint val) {
        ListNode* temp=head;
        ListNode* ans;
        if(head==NULL){
            return NULL;
        }
        while(temp->val==val){
            if(temp->next==NULL){
                return NULL;
            }
            temp=temp->next;
        }
        ans=temp;
        while(temp->next!=NULL){
            if(temp->next->val==val){
              ListNode* left=temp;
                while(temp->next->val==val){
                    
                   temp=temp->next
                    if(temp->next==NULL){
                        left->next=NULL;
                        return ans;
                    }
                }
                left->next=temp->next;
            }
            else{
                temp=temp->next;
            }
            
            
        }
        return ans;
        
    }
};

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