June 21 Daily

DataStructures/PriorityQueue/LC23(Hard).cpp

@@ -0,0 +1,48 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+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) {}
+};
+
+// 23. 合并K个升序链表
+
+// 给你一个链表数组，每个链表都已经按升序排列。
+
+// 请你将所有链表合并到一个升序链表中，返回合并后的链表。
+
+class cmp{
+public:
+    bool operator()(ListNode* a,ListNode* b){
+        return a->val>b->val;
+    }
+};
+class Solution {
+public:
+    ListNode* mergeKLists(vector<ListNode*>& lists) {
+        priority_queue<ListNode*,vector<ListNode*>,cmp> pq;
+        for(ListNode*& node : lists){
+            if(node){
+                pq.push(node);
+            }
+        }
+        ListNode dummyHead = ListNode();
+        ListNode* pre = &dummyHead;
+
+        while(!pq.empty()){
+            pre->next = pq.top();
+            pre = pre->next;
+            ListNode* next = pq.top()->next;
+            pq.pop();
+            if(next){
+                pq.push(next);
+            }
+        }
+        return dummyHead.next;
+    }
+};