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Weights and measures: the containers problem
Published October 16, 2026.
This module is a great classic of brain teasers: with containers of different capacities and no graduation, you must obtain a precise quantity. Here the contents are sand, and the level to reach is shown by a mark on the target container.
The gestures
Two or three containers stand in front of you. Drag a container onto the source to fill it, onto the drain to empty it, or onto another container to pour into it. When the level is the one of the mark, pull the lever: it is an attempt, and a wrong level costs 15 seconds.
What to know about pouring
Pouring from one container into another stops in one of two cases: the source container is empty, or the destination container is full. Each pour is therefore entirely determined: there is no chance involved. The state of the game boils down to the quantity in each container: a list of two or three numbers.
A method to avoid going in circles
Write down the states you have already visited so as not to return to them. From the starting state (everything empty), there are only a few possible moves: fill, empty or pour. Explore them in order and see where they lead. A good reflex is to always fill the biggest container and pour into the smallest, then empty that one and start again: the quantities you get this way are differences of multiples of the two capacities.
Rest assured: the box is always built to have a solution, and it is the length of the shortest path that gives the module its difficulty.
Why it is a good brain teaser
This type of problem has been known for centuries: measuring a precise quantity with two containers without graduation. It illustrates a simple and powerful idea: you can get any quantity that is a combination of multiples of the capacities, limited by the size of the containers. With three containers the possibilities widen, but the method stays the same: visit the states one by one, never repeating one you have already seen.
In the game, the mark on the target container tells you exactly which level to aim for: no need to look for another quantity.
Practise in the game
The game's tutorials, with no clock and no penalty, let you practise this subject: