*Leetcode 23. 合并K个升序链表

Posted 2023-03-05 Z-Pilgrim

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/**
 * Definition for singly-linked list.
 * struct ListNode 
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) 
 *     ListNode(int x) : val(x), next(nullptr) 
 *     ListNode(int x, ListNode *next) : val(x), next(next) 
 * ;
 */
class Solution 
public:
    ListNode* merge2List(ListNode*l1, ListNode*l2) 
        if(!l1) return l2;
        if(!l2) return l1;
        ListNode *ret = NULL, *tail = NULL;
        while(l1 && l2) 
            ListNode *cur = NULL;
            if(l1->val < l2->val) 
                cur = l1;
                l1 = l1->next;
             else 
                cur = l2;
                l2 = l2->next;
            
            if(!ret) 
                ret = tail = cur; 
             else 
                tail->next = cur;
                tail = tail->next; 
            
        
        if(l1) tail->next = l1;
        if(l2) tail->next = l2;
        return ret;
    


    ListNode* mergeKLists(vector<ListNode*>& lists, int l, int r) 
        if(l > r) return NULL;
        if(l == r) return lists[l];
        if(l + 1 == r) return merge2List(lists[l], lists[r]);
        ListNode*l_rslt = mergeKLists(lists, l, l + (r-l)/2);
        ListNode*r_rslt = mergeKLists(lists, l+(r-l)/2+1, r);
        return merge2List(l_rslt, r_rslt);
    


    ListNode* mergeKLists(vector<ListNode*>& lists) 
        if(lists.size() == 0) return NULL;
        return mergeKLists(lists, 0, lists.size()-1);
    
;