A personal collection of classic data-structure implementations in C, Java and Python: lists, stacks, queues, hash tables, skip lists, graphs, heaps and trees, each built from first principles with its own runnable test driver. It started as coursework for the Estructura de Dades (Data Structures) course of the URV Computer Science degree and was later extended with a Python list hierarchy and a Java double-ended queue. The C tree uses one makefile per module, the Java tree is an IntelliJ project, and the Python tree is a small object-oriented List / LinkedList hierarchy.