23. Merge k Sorted Lists

Author: SteffiKeranJ

mergeKLists.cpp

@@ -0,0 +1,40 @@
+/**
+ * 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) {
+        map<int, int> freq;
+        for(int i = 0 ; i < lists.size(); ++i) {
+            auto node = lists[i]; // take the head
+            while(node) {
+                // take the node's val
+                int temp = node ->val;
+                // put it in the ordered map
+                freq[temp]++;
+                node = node->next;
+            }
+        }
+        ListNode dummy(0); // create new linked list
+        ListNode* tail = &dummy;
+        for(auto i : freq) {
+            while(i.second!=0) {
+                // create a node for every item
+                ListNode* newnode = new ListNode(i.first);
+                // add it to tail
+                tail->next = newnode;
+                tail = tail->next;
+                // decrement the freq
+                i.second--;
+            }
+        }
+        return dummy.next;
+    }
+};