Added Reverse_First_K_Elements

Data Structures/Queues/Reverse_First_K_Elements.cpp

@@ -0,0 +1,70 @@
+#include<iostream>
+using namespace std;
+int front = -1, rear= -1;
+int queue[100],stack[100],top= -1,size;
+
+void enqueue(int x)
+{
+    if(front == -1)
+        front =0;
+    rear ++ ;
+    queue[rear]= x;
+
+}
+int dequeue(){
+    if(front >rear || front == -1)
+        return INT_MIN;
+    return queue[front++];
+}
+void reverseK(int k)
+{
+    while(front<=rear && k--){
+        int x=dequeue();
+        stack[++top]= x;
+    }
+    while(top!= -1){
+        int x = stack[top--];
+        enqueue(x);
+    }
+    for (int i = front; i < rear-front-k; i++) {
+        int x= dequeue();
+        enqueue(x);
+    }
+
+    return;
+}
+
+void display()
+{
+    if(front > rear || front ==-1){
+        cout<< "cannot dispay";
+        return;}
+    int i = front;
+    while(i <=rear){
+        cout<< queue[i++]<<" ";
+    }
+}
+
+int main ()
+{
+    int q;
+    cout<<"Enter the size of Queue: ";
+    cin>> size;
+    cout<< "\nEnter the elements of Queue: ";
+
+    for (int i=0;i<size;i++)
+    {
+        cin>>q;
+        enqueue(q);
+    }
+    int k ;
+    cout<<"\nEnter value of k: ";
+    cin>> k;
+    cout<< "\nFirst "<< k << " elements reversed: ";
+    reverseK(k);
+    display();
+    cout<<endl;
+
+    return 0;
+
+}