题解 | #合并k个已排序的链表#

思路：合并两个链表，遍历给定的数组。

 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
   ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
    ListNode* ans= new ListNode(-1);
    ListNode* head = ans;
    while (l1 != NULL && l2 != NULL) {
        if (l1->val < l2->val) {
            head->next = l1;
            l1 = l1->next;
        }
        else {
            head->next = l2;
            l2 = l2->next;
        }
        head = head->next;
    }
    head->next = l1 == NULL ? l2 : l1;
    return ans->next;
}
ListNode* mergeKLists(vector<ListNode*>& lists) {
    ListNode* ans = NULL;
    for (int i = 0; i < lists.size(); i++) {
        ans=mergeTwoLists(ans, lists[i]);
    }
    return ans;
}

};