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Day-078.cpp
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Day-078.cpp
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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) {}
* };
*/
using Heap = set<pair<int , ListNode*>>;
class Solution {
public:
ListNode* mergeKLists(vector<ListNode*>& lists) {
Heap h;
ListNode* temp, *res;
temp = res = nullptr;
const int &k = lists.size();
for (int i = 0; i < k; ++i) {
if (lists[i] != nullptr) {
h.insert(make_pair(lists[i] -> val, lists[i]));
}
}
while (h.empty() == false) {
ListNode* x = (*h.begin()).second;
if (res == nullptr) {
res = temp = x;
} else {
temp -> next = x;
temp = temp -> next;
}
h.erase(h.begin());
if (x -> next != nullptr) {
x = x -> next;
h.insert(make_pair(x -> val, x));
}
}
return res;
}
};