Edit distance

Unit-cost insertion/deletion/substitution over exact Text code points; no transposition, folding, or normalization. Empty-to-nonempty distance is its code-point count. Prototype uncached recursion; final O(nm) DP with O(min(n,m)) auxiliary memory. Preserve strings.

Public signatures:

Int prototype(const Text& left,const Text& right);
Int solve(const Text& left,const Text& right);

Compile and run from this directory:

c++ -std=c++20 -O2 -Wall -Wextra -pedantic -pthread main.cpp -o practice
./practice --stage prototype
./practice --stage final

Edit exercise.hpp. Both stages start unfinished and must report failures until implemented. Keep main.cpp as the executable contract. The runner returns nonzero for a failed check, an unexpected exception, an invalid stage, or an empty suite. C++20 and only the standard library are required.