Hopefully you have noticed some characteristics of these problems:
The number of steps it takes to get to a solution varies.
There are only a few actions that can be taken: filling a pitcher, pouring from one pitcher to another, and emptying a pitcher into the river.
A few less obvious characteristics:
There may be more than one way to solve the problem, e.g. problem two could also be solved like this: 1) Fill the ten-litre pitcher, 2) pour from it into the five-litre pitcher, 3) pour from it into the two-litre pitcher, 4) empty the two-litre pitcher into the river, 5) pour from the ten-litre pitcher again into the two-litre pitcher. Now there is one litre of water left in the ten-litre pitcher. This solution is longer than the one we saw before, and we naturally prefer shorter solutions, so let's agree that we would like the shortest solution possible.
There may be no solution, e.g. "Given a five-litre pitcher and a ten-litre pitcher measure one litre of water."
A solution may involve more than one pitcher, e.g. the problem " You have a three-litre pitcher and a seven-litre pitcher. You need ten litres of water." The solution is to fill them both, and now have you have the required ten liters of water in both pitchers combined.