ListNode示例

ListNode* partition(ListNode* head, int x) {    ListNode res(0), mid(0);    if (!head) return NULL;    ListNode* small=&res;    ListNode* big=&mid;        while (head) {        if (head->val < x) {            small->next = head;            small = small->next;        }        else {            big->next = head;            big = big->next;        }        head = head->next;    }    big->next = NULL;    small->next = mid.next;    return res.next;}