Special Solution of Simple cases

Special Solution of Simple cases

In addition to putting a simple case first, it can also be efficient to solve simple cases differently to the general case. When solving a problem, simple cases can often be solved by specially designed fast functions. These “special solutions” can involve table lookup of precalculated values (e.g. storing the first ten factorials in an array) or just a fast algorithm for small cases (e.g. sorting less than five numbers quickly).

In general, the special solution of simple cases will give some speed increase if the simple cases are fairly common. The advantage of simple case precalculation over full precalculation is flexibility — it is not limited to those values that can be stored in a fixed size table.

The use of table lookup for simple cases for the factorial function is shown below. The use of the method here gives speed increase for all cases, not just the simple ones, because the recursive definition of factorial eventually breaks the problem down to a simple case.

    int factorial_precalc(int n)
    {
        const int NUM_PRECALC = 5; // How many
        static int s_precalc[NUM_PRECALC + 1] = 
            { 1, 1, 2, 6, 24, 120 };

        if (n <= NUM_PRECALC)
            return s_precalc[n];
        else
            return n * factorial_precalc(n - 1);
    }

• Next: • Up: Table of Contents • Buy: Generative AI in C++: Coding Transformers and LLMs

The new AI programming book by Aussie AI co-founders: AI coding in C++ Transformer engine speedups LLM models Phone and desktop AI Code examples Research citations Get your copy from Amazon: Generative AI in C++