Added C++ code for ternary search

Author: anvitareddy6

data_structures/C++/ternary_search.cpp

@@ -0,0 +1,55 @@
+#include <iostream>
+using namespace std;
+int ternarySearch(int l, int r, int key, int ar[])
+
+{
+    while (r >= l) {
+
+        int mid1 = l + (r - l) / 3;
+        int mid2 = r - (r - l) / 3;
+
+        if (ar[mid1] == key) {
+            return mid1;
+        }
+        if (ar[mid2] == key) {
+            return mid2;
+        }
+
+
+        if (key < ar[mid1]) {
+
+            // The key lies in between l and mid1 
+            r = mid1 - 1;
+        }
+        else if (key > ar[mid2]) {
+
+            // The key lies in between mid2 and r 
+            l = mid2 + 1;
+        }
+        else {
+
+            // The key lies in between mid1 and mid2 
+            l = mid1 + 1;
+            r = mid2 - 1;
+        }
+    }
+    return -1;
+}
+int main()
+{
+ int len;
+cin>>len;
+int ar[len];
+for(int i=0;i<len;i++){
+        cin>>ar[i];
+}
+int key;
+cin>>key;
+int l=0;
+int r=len-1;
+int p=0;
+     p = ternarySearch(l, r, key, ar);
+
+    cout << "Index of "<<key<<" is " << p << endl;
+}
+