每日一题 LCR 078. 合并 K 个升序链表

LCR 078. 合并 K 个升序链表

使用二分法就可以解决

class Solution {
public:
    ListNode* mergeKLists(vector<ListNode*>& lists) {

        int n = lists.size();

        if(n == 0){
            return nullptr;
        }
        ListNode* ans ;

        ans = binMerge(lists,0,n-1);
        return ans;
    }

    ListNode* binMerge(vector<ListNode*> &lists,int l,int r ){
        //cout<<l<<" "<<r<<endl;
        if(l > r){
            return nullptr;
        }
        if(l == r){
            return lists[l] ;
        }
        int mid = (l+r)/2;
        ListNode* ll = binMerge(lists,l,mid);
        ListNode* rr = binMerge(lists,mid+1,r);

        return mergeListTwo(ll,rr);
    }

    ListNode* mergeListTwo(ListNode* l, ListNode* r){
        
        ListNode* dummy = new ListNode(0);
        ListNode* h = dummy;
        while(l && r){
            if(l->val > r->val){
                h->next = r;
                r = r->next;
            }else{
                h->next = l;
                l = l->next;
            }
            h = h->next;
        }
        if(l){
            h->next = l;
        }
        if(r){
            h->next = r;
        }
        return dummy->next;
    }
};