ABOUT THIS ARCHIVE
A place for problems that stay with you.
I am ZhangWeilong. I like problems that are easy to state, difficult to see through, and satisfying to understand. This library is where I keep the ones I want to revisit.
It is not a catalogue of everything I have solved. Some entries are complete, some are working notes, and some remain deliberately open. The common thread is that each contains an idea worth remembering.
What belongs here
Mathematical puzzles, logic games, geometry, probability, number theory, algorithms, board problems, and collections such as Project Euler or IBM Ponder This. Occasionally a puzzle grows into a longer note; those live beside the archive rather than inside the solution.
A small editorial rule
The interface should recede. The problem, diagram, and argument should hold the page.
That is why this site is quiet, mostly typographic, and intentionally light on decoration.