Added to linked-list

Author: sr-sweta

Data Structures/Linked Lists/Singly Linked List/merge_k_sorted_linkedlist.cpp

@@ -0,0 +1,90 @@
+/*You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.
+Number of nodes in a linked-list can be 0.
+Merge all the linked-lists into one sorted linked-list and return it.
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+struct ListNode
+{
+    int val;
+    ListNode *next;
+    ListNode(int n)
+    {
+        val = n;
+        next = NULL;
+    }
+};
+
+void printList(ListNode* head){
+	int i = 0;
+	while(head){
+		cout<<head->val<<" ";
+		head = head->next;
+	}
+}
+
+//Go on merging 2 linked list into 1 
+ListNode* mergeTwoLists(ListNode* l1,ListNode* l2) {
+    if(!l1) return l2;
+    if(!l2) return l1;
+    if(l1->val<l2->val){
+       l1->next=mergeTwoLists(l1->next,l2);
+       return l1;
+    }
+    else{
+        l2->next=mergeTwoLists(l1,l2->next);
+        return l2;
+    }
+}
+ 
+   
+ListNode* mergeKLists(vector<ListNode*>& lists) {
+    if(!lists.size()) return NULL;
+    int l=lists.size();
+    while(l>1){
+        for(int i=0;i<l/2;i++){
+        	//Passing 2 linked-list head to merge them
+            lists[i]=mergeTwoLists(lists[i],lists[l-1-i]);
+        }
+        l=(l+1)/2;
+    }
+    return lists.front();
+}
+    
+int main()
+{
+    int NumOfList, NumOfNodes, nl, nn, data;
+    vector<ListNode*> headList;
+    //cout<<"Enter no of list\n";
+    cin>>NumOfList;
+    nl = NumOfList;
+    
+    while(nl--){
+    	//cout<<"Enter no of nodes\n";
+    	cin>>NumOfNodes;
+    	nn = NumOfNodes;
+    	ListNode* head = NULL;
+    	ListNode* tail = head;
+    	int i = NumOfNodes;
+    	while(nn--){
+    		cin>>data;
+    		if(nn == NumOfNodes-1){
+    			head = new ListNode(data);
+    			tail = head;
+			}
+			else{
+				tail->next = new ListNode(data);
+				tail = tail->next;
+			}
+			
+		}
+		headList.push_back(head);
+	}
+	ListNode* finalHead = mergeKLists(headList);
+	printList(finalHead);
+    return 0;
+}
+//No extra space used.
+