/**
 * 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* mergeKLists(vector<ListNode*>& lists) {
        ListNode newList;
        ListNode*head=&newList;
        while(true){
            int min=-1,minval=0x3fffffff;
            for(int i=0;i<lists.size();i++){
                ListNode*l=lists[i];
                if(l && l->val < minval){
                    min=i;
                    minval=l->val;
                }
            }
            if(min<0)break;
            head->next=lists[min];
            lists[min]=lists[min]->next;
            head=head->next;
        }
        head->next=nullptr;
        return newList.next;
    }
};

class Solution {
public:
    char findTheDifference(string s, string t) {
        map<char, int>count;
        for(auto&&c:s){
            count[c]++;
        }
        for(auto&&c:t){
            count[c]--;
        }
        return find_if(count.begin(),count.end(),[&](auto it){return it.second!=0;})->first;
    }
};