163494

Crossing the bridge:
A: Smallest number
B:Second smallest number
C:Third smallest number
D: Largest number

Strategy 1:
A and B first cross the bridge
A comes back
C and D cross the bridge
B comes back
A and B cross the bridge

Strategy 2:
A and B cross the bridge
A comes back
A and C cross the bridge
A comes back
A and D cross the bridge

Solution:
If the numbers are all different, then you need to use Strategy A

If there are 3 numbers that are the same and one is bigger than the others then you can use either strategy

If There are 3 numbers that are the same and one is smaller than the others, you need to use strategy 2

Any other number composition is solved with Strategy A