Topology optimization methods:
Continuum (density) approach
Start with a bounding envelope full of material. Where the material is relatively un-stressed, reduce the density and gradually steer the solution towards one that is just black and white (so that there is material or there isn't).
Ground structure approach
Start with a lattice-grid of beams connecting nodes. Selectively turn beams on or off depending on how stressed they are until you converge on the optimal solution.
Describe the geometry of your design with a small number of variables. Change the variables until the design converges to the optimal (determined by some optimality criteria.) In this case, the length of a tuning fork is adjusted until the natural frequency is exactly 440Hz.