LinkedListNode* mergeLists(LinkedListNode* a, LinkedListNode *b){
    // assumes length a >= length b    
    LinkedListNode *curNode=a, *nextNode=b, *nextNextNode;
    while(curNode != NULL && nextNode!=NULL){
        nextNextNode = curNode->next;
        curNode->next = nextNode;
        curNode = nextNode;
        nextNode = nextNextNode;
    }
    return a;
}

LinkedListNode* reverseList(LinkedListNode* a){
    LinkedListNode *head = NULL, *curNode=a, *nextNode;
    while(curNode!=NULL){
        nextNode = curNode->next;
        curNode->next = head;
        head = curNode;
        curNode = nextNode;
    }
    return head;
}

LinkedListNode* getLowerMiddleNode(LinkedListNode* a){
    LinkedListNode *singleJump=a, *doubleJump = a;
    while(doubleJump->next != NULL && doubleJump->next->next != NULL){
        singleJump = singleJump->next;
        doubleJump = doubleJump->next->next;
    }
    return singleJump;
}

LinkedListNode* reverseZigZagMerge(LinkedListNode* a){
    if(a == NULL) return NULL;
    LinkedListNode *lowerMiddelNode = getLowerMiddleNode(a);
    LinkedListNode *secondHalf = lowerMiddelNode->next;
    lowerMiddelNode->next = NULL;
    return mergeLists(a,reverseList(secondHalf));
}