There is an Island of puzzles called puzzles-world where numbers 1 - 9 want to cross a river.
There is a single boat that can take numbers from one side to the other.
However, maximum 3 numbers can go at a time and of course,
the boat cannot sail on its own so one number must come back after reaching to another side.
Also, the sum of numbers crossing at a time must be a square number.
You need to plan trips such that minimum trips are needed.
How many minimum trips are needed ?