Odd Even Linked List Solutions in C++

// Source : https://leetcode.com/problems/odd-even-linked-list/
// Author : Hao Chen
// Date   : 2016-01-16



/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if (!head) return head;
        ListNode* pOdd = head;
        ListNode* p = head->next;
        ListNode* pNext = NULL;
        while(p && (pNext=p->next)) {
            
            p->next = pNext->next;
            pNext->next = pOdd->next;
            pOdd->next = pNext;
            
            p = p->next;
            pOdd = pOdd->next;
        
        }
        return head;
    }
};

/// Source : https://leetcode.com/problems/odd-even-linked-list/description/
/// Author : liuyubobobo
/// Time   : 2018-10-01

#include <iostream>

using namespace std;


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


/// Split the Linked List into two and then merge
/// Time Complexity: O(n)
/// Space Complexity: O(1)
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {

        if(head == NULL || head->next == NULL || head->next->next == NULL)
            return head;

        ListNode* dummyHead1 = new ListNode(-1);
        ListNode* dummyHead2 = new ListNode(-1);
        ListNode* p1 = dummyHead1;
        ListNode* p2 = dummyHead2;
        ListNode* p = head;
        for(int i = 0; p; i ++)
            if(i % 2 == 0){
                p1->next = p;
                p = p->next;
                p1 = p1->next;
                p1->next = NULL;
            }
            else{
                p2->next = p;
                p = p->next;
                p2 = p2->next;
                p2->next = NULL;
            }

        p1->next = dummyHead2->next;
        ListNode* ret = dummyHead1->next;

        delete dummyHead1;
        delete dummyHead2;
        return ret;
    }
};


int main() {

    return 0;
}

/// Source : https://leetcode.com/problems/odd-even-linked-list/description/
/// Author : liuyubobobo
/// Time   : 2018-10-01

#include <iostream>

using namespace std;


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


/// Split the Linked List into two and then merge
/// Keep one in original Linked List
///
/// Time Complexity: O(n)
/// Space Complexity: O(1)
class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {

        if(head == NULL || head->next == NULL || head->next->next == NULL)
            return head;

        ListNode* dummyHead2 = new ListNode(-1);
        ListNode* p2 = dummyHead2;
        ListNode* p = head;
        while(p->next){
            p2->next = p->next;
            if(p->next->next == NULL){
                p->next = NULL;
                break;
            }
            p->next = p->next->next;
            p = p->next;
            p2 = p2->next;
            p2->next = NULL;
        }

        p->next = dummyHead2->next;
        delete dummyHead2;
        return head;
    }
};


int main() {

    return 0;
}