Remove Linked List Elements Solutions in C++

// Source : https://leetcode.com/problems/remove-linked-list-elements/
// Author : Hao Chen
// Date   : 2015-06-09



/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        static ListNode dummy(-1);
        dummy.next = head;
        ListNode *p = &dummy;
        
        while( p->next) {
            if (p->next->val == val) {
                p->next = p->next->next;
            }else{
                p = p->next;
            }
        }
        
        return dummy.next;
    }
};

/// Source : https://leetcode.com/problems/remove-linked-list-elements/description/
/// Author : liuyubobobo
/// Time   : 2017-11-15

#include <iostream>

using namespace std;

///Definition for singly-linked list.
struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

/// LinkedList Test Helper Functions
ListNode* createLinkedList(int arr[], int n){

    if(n == 0)
        return NULL;

    ListNode* head = new ListNode(arr[0]);
    ListNode* curNode = head;
    for(int i = 1 ; i < n ; i ++){
        curNode->next = new ListNode(arr[i]);
        curNode = curNode->next;
    }

    return head;
}

void printLinkedList(ListNode* head){

    if(head == NULL){
        cout << "NULL" << endl;
        return;
    }

    ListNode* curNode = head;
    while(curNode != NULL){
        cout << curNode->val;
        if(curNode->next != NULL)
            cout << " -> ";
        curNode = curNode->next;
    }

    cout << endl;

    return;
}

void deleteLinkedList(ListNode* head){

    ListNode* curNode = head;
    while(curNode != NULL){
        ListNode* delNode = curNode;
        curNode = curNode->next;
        delete delNode;
    }

    return;
}


/// Linear Scan with dummy head
/// Time Complexity: O(n)
/// Space Complexity: O(1)
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {

        ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;

        ListNode* cur = dummyHead;
        while(cur->next != NULL){
            if(cur->next->val == val){
                ListNode* delNode = cur->next;
                cur->next = delNode->next;
                delete delNode;
            }
            else
                cur = cur->next;
        }

        ListNode* retNode = dummyHead->next;
        delete dummyHead;

        return retNode;
    }
};


int main() {

    int arr[] = {1, 2, 6, 3, 4, 5, 6};
    int n = sizeof(arr) / sizeof(int);

    ListNode* head = createLinkedList(arr, n);
    printLinkedList(head);

    Solution().removeElements(head, 6);
    printLinkedList(head);

    deleteLinkedList(head);

    return 0;
}

/// Source : https://leetcode.com/problems/remove-linked-list-elements/description/
/// Author : liuyubobobo
/// Time   : 2018-09-17

#include <iostream>

using namespace std;

///Definition for singly-linked list.
struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};


/// Recursive
/// Time Complexity: O(n)
/// Space Complexity: O(n)
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {

        if(!head)
            return head;

        if(head->val == val){
            ListNode* node = head->next;
            delete head;
            return removeElements(node, val);
        }

        head->next = removeElements(head->next, val);
        return head;
    }
};


int main() {

    return 0;
}