In Dijkstra's paper "Humble Programmer", he mentions that he gave some volunteers a problem to solve:
“I have run a little programming experiment with really experienced volunteers, but something quite unintended and quite unexpected turned up. None of my volunteers found the obvious and most elegant solution. Upon closer analysis this turned out to have a common source: their notion of repetition was so tightly connected to the idea of an associated controlled variable to be stepped up, that they were mentally blocked from seeing the obvious. Their solutions were less efficient, needlessly hard to understand, and it took them a very long time to find them.”
What was the problem Dijkstra gave to the volunteers? What were the solutions?