NC51 #合并k个已排序的链表#

思路和合并两个链表一样，多写个for循环而已

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if(l1 == nullptr) return l2;
        if(l2 == nullptr) return l1;
        ListNode* pHead = nullptr;
        if(l1->val < l2->val)
            pHead = l1, l1 = l1->next;
        else pHead = l2, l2 = l2->next;
        ListNode* pTail = pHead;
        while(l1 != nullptr && l2 != nullptr)
        {
            if(l1->val < l2->val)
                pTail->next = l1, l1 = l1->next;
            else
                pTail->next = l2, l2 = l2->next;
            pTail = pTail->next;
        }
        if(l1 == nullptr) pTail->next = l2;
        else pTail->next = l1;
        return pHead;
    }
    ListNode *mergeKLists(vector<ListNode *> &lists) {
        int len = lists.size();
        if(len == 0) return nullptr;
        ListNode * temp = lists[0];
        for(int i = 1; i < len; i++)
            temp = mergeTwoLists(temp, lists[i]);
        return temp;
    }
};