4. What is meant by the optimal substructure property in the context of dynamic programming. Using the dynamic programming technique, devise an algorithm for finding the least cost way to convert a given string X to another string Y . The allowed operations are INSERT, DELETE, REPLACE, and COPY with costs of 2, 3, 4, and 1 respectively for each of the above operations. Show the recurrence relation and then write a memoized program. Finally, add enough steps to be able to print the solution.