The longest common subsequnce (LCS) problem is a dual problem of the shortest edit distance (SED) problem. The solution to these problems are used in open source file comparison tools such as WinMerge and DiffMerge. In 1974, Hirshberg published a reasonably space and time efficient solution to these problems. This talk will cover the incremental development and implementation of Hirshberg's algorithm in Lua, including trade-offs and design decisions along the way. The final algorithm implementation can be used for customized comparsion of files, or other applications, as needed.