Create main.cpp

Author: JawadSher

19 - Heap Data Structure Problems/13 - Merge K Sorted Lists/main.cpp

@@ -0,0 +1,48 @@
+/**
+ * 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 compare{
+    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*>, compare> pq; 
+
+        int k = lists.size();
+        
+        if(k == 0) return NULL;
+        for(int i = 0; i < k; i++) if(lists[i] != NULL) pq.push(lists[i]);
+        
+        ListNode* head = NULL;
+        ListNode* tail = NULL;
+
+        while(pq.size() > 0){
+            ListNode* top = pq.top();
+            pq.pop();
+
+            if(head == NULL){
+                head = top;
+                tail = top;
+            }else{
+                tail -> next = top;
+                tail = top;
+            }
+
+            if(top -> next != NULL) pq.push(top -> next);
+        }
+
+        return head;
+    }
+};