6. For this question, you need to use C++ string (add #include at the top of your .cpp file). There is a very short introduction to C++ string in textbook Section 2.3. Basically, C++ string is an object and it behaves very similarly to strings in other Object Oriented languages such as Java, Python. The following code fragment will help you with all the syntax you need to deal with C++ string in this question. Then, you will have to figure out the algorithm and its implementation to solve this question. string s1 = "hello"; cout