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struct ListNode {    int val;    struct ListNode* next;};struct ListNode* middleNode(struct ListNode* head) {    struct ListNode* fast = head, *slow = head;    while (fast && fast->next) {        slow = slow->next;        fast = fast->next->next;    }    return slow;}

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struct ListNode {    int val;    struct ListNode* next;};struct ListNode* getKthFromEnd(struct ListNode* head, int k) {    struct ListNode* fast = head, *slow = head;    while (k--) {        if (fast == NULL) {            return NULL;        }        fast = fast->next;    }    while (fast) {        fast = fast->next;        slow = slow->next;    }    return slow;}

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struct ListNode {    int val;    struct ListNode* next;};struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {    struct ListNode* head = NULL, *tail = NULL;    if (l1 == NULL) {        return l2;    }    if (l2 == NULL) {        return l1;    }    if (l1->val < l2->val) {        head = tail = l1;        l1 = l1->next;    } else {        head = tail = l2;        l2 = l2->next;    }    while (l1 && l2) {        if (l1->val < l2->val) {            tail->next = l1;            l1 = l1->next;        } else {            tail->next = l2;            l2 = l2->next;        }        tail = tail->next;    }    if (l1) {        tail->next = l1;    }    if (l2) {        tail->next = l2;    }    return head;}

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struct ListNode {    int val;    struct ListNode* next;};struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {    struct ListNode* head = NULL, *tail = NULL;    head = tail = (struct ListNode*)malloc(sizeof(struct ListNode));    tail->next = NULL;    while (l1 && l2) {        if (l1->val < l2->val) {            tail->next = l1;            l1 = l1->next;        } else {            tail->next = l2;            l2 = l2->next;        }        tail = tail->next;    }    if (l1) {        tail->next = l1;    }    if (l2) {        tail->next = l2;    }    struct ListNode* node = head;    head = head->next;    free(node);    return head;}

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