Remove Linked List Elements Problem


Description

LeetCode Problem 203.

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:

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

Example 2:

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

Example 3:

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

Constraints:

  • The number of nodes in the list is in the range [0, 10^4].
  • 1 <= Node.val <= 50
  • 0 <= val <= 50


Sample C++ Code

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/**
 * 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* head, int val) {
        if (head == NULL)
            return head;
        
        ListNode* curr = head;
        
        while (curr->next != NULL) {
            if (curr->next->val == val) {
                curr->next = curr->next->next;
            } else {
                curr = curr->next;
            }
        }
        
        if (head->val == val)
            head = head->next;
        
        return head;
    }
};




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