diff --git a/cpp/23-Merge-K-Sorted-Lists.cpp b/cpp/23-Merge-K-Sorted-Lists.cpp
new file mode 100644
index 000000000..7f61d8afa
--- /dev/null
+++ b/cpp/23-Merge-K-Sorted-Lists.cpp
@@ -0,0 +1,51 @@
+/**
+ * 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;
+        
+        for(int i=0;i<lists.size();i++){
+            if(lists[i]!=NULL){
+                pq.push(lists[i]);
+            }
+        }
+        
+        if(pq.empty()){
+            return NULL;
+        }
+        
+        ListNode* dummy=new ListNode;
+        ListNode* last=dummy;
+        
+        while(!pq.empty()){
+            ListNode* curr=pq.top();
+            pq.pop();
+            
+            last->next=curr;
+            last=last->next;
+            
+            if(curr->next!=NULL){
+                pq.push(curr->next);
+            }
+        }
+        return dummy->next;
+    }
+};
\ No newline at end of file
diff --git a/cpp/25-Reverse-Nodes-in-k-Group.cpp b/cpp/25-Reverse-Nodes-in-k-Group.cpp
new file mode 100644
index 000000000..d7694611d
--- /dev/null
+++ b/cpp/25-Reverse-Nodes-in-k-Group.cpp
@@ -0,0 +1,47 @@
+/**
+ * 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* reverseKGroup(ListNode* head, int k) {
+        
+        if(head==NULL || head->next==NULL){
+            return head;
+        }
+        
+        ListNode* res=new ListNode(0);
+        res->next=head;
+        ListNode* start=res;
+        stack<ListNode*> st;
+        ListNode* prev=NULL;
+        while(head!=NULL){
+            ListNode* temp=head;
+            while(st.size()<k && head!=NULL){
+                st.push(head);
+                head=head->next;
+            }
+            if(st.size()==k){
+                while(!st.empty()){
+                    prev=st.top();
+                    prev->next=NULL;
+                    st.pop();
+                    start->next=prev;
+                    start=start->next;
+                }
+            }
+            else{
+                start->next=temp;
+                return res->next;
+            }
+        }
+        prev->next=NULL;
+        return res->next;
+    }
+};
\ No newline at end of file
diff --git a/cpp/30-Substring-with-Concatenation-of-All-Words.cpp b/cpp/30-Substring-with-Concatenation-of-All-Words.cpp
new file mode 100644
index 000000000..56940b581
--- /dev/null
+++ b/cpp/30-Substring-with-Concatenation-of-All-Words.cpp
@@ -0,0 +1,28 @@
+class Solution {
+public:
+    vector<int> findSubstring(string s, vector<string>& words) {
+        
+        unordered_map<string,int> mp;
+        for(string word:words){
+            mp[word]++;
+        }
+        
+        int slen=s.size();
+        int wlen=words.size();
+        int len=words[0].size();
+        
+        vector<int> ans;
+        for(int i=0;i<slen-wlen*len+1;i++){
+            string temp=s.substr(i,wlen*len);
+            unordered_map<string,int> seen;
+            for(int j=0;j<temp.size();j+=len){
+                string curr=temp.substr(j,len);
+                seen[curr]++;
+            }
+            if(seen==mp){
+                ans.push_back(i);
+            }
+        }
+        return ans;
+    }
+};
\ No newline at end of file