A substring of some character string is a contiguous sequence of characters in that string (which is different than a subsequence, of course). Suppose you are given two character strings, X and Y , with respective lengths n and m. Describe an efficient algorithm for finding a longest common substring of X and Y .For each algorithm:i. Explain the main idea and approach. Write appropriate pseudo-code. Trace it on at least three different examples, including at least a canonical case and two corner cases. iv. Give a proof of correctness. v. Give a worst-case asymptotic running time analysis.