add 23

Author: rustykitty

0023-merge-k-sorted-lists.cpp

@@ -0,0 +1,44 @@
+/*
+23. Merge k Sorted Lists
+
+Submitted: December 12, 2024
+
+Runtime: 0 ms (beats 100.00%)
+Memory: 18.28 MB (beats 84.05%)
+*/
+
+/**
+ * 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) {
+        auto cmp = [](ListNode* a, ListNode* b) { return std::greater<int>()(a->val, b->val); };
+        priority_queue<ListNode*, vector<ListNode*>, decltype(cmp)> pq;
+        for (ListNode* list : lists) {
+            if (list != nullptr) pq.push(list);
+        }
+        ListNode* newHead = nullptr;
+        ListNode* newTail = nullptr;
+        while (!pq.empty()) {
+            ListNode* p = pq.top();
+            pq.pop();
+            if (p->next != nullptr) pq.push(p->next);
+            if (newHead == nullptr) {
+                newHead = p;
+                newTail = p;
+            } else {
+                newTail->next = p;
+                newTail = newTail->next;
+            }
+        }
+        return newHead;
+    }
+};