For easy identification without calculation,In oneway slab
main reinforcement provided in the shorter direction and
distribution will be longer side.In two way slab Both side
main reinforcement will be there and mainbar also act as a
distribution bar.

silambarasan is wrong... In all drawings main reinforcement will be in shorter direction. We cannot decide only by using this option. What if all the rods, say for example 12 mm dia bar both sides each way is given... This again depends on the longer and the shorter span.
If ly/lx < 2 then it is a 2 way slab..This is the main criteria for identifying 2 way slab or 1 way slab.
According to structural point of view,
In 2 way slab loads will be carried in 2 directions, so main reinforcement is provided in 2 ways.
In 1 way slab loads will be carried in 1 direction, so main reinforcement is provided in 1 way.

In two way slab reinforcement is in 2 layer @ T&B of equal dia is provided whereas in one way slab main reinf tats reinf of higher dia is provided along shorter span and nominal dia reing is provided along longer span

see reinforcement spacing. for distribution reinforcement
spacing is very high. we provide nominal reinforcement
subjected to maximum of 45o mm. then categorise it as one
way slab. otherwise two way slab.