I'm having the exact same problem and I really can't understand why the lift stops at floor 3 at the end.

SO the case is:

Capacity: 4

4: [2]
3: [4, 1, 0, 4]
2: [3, 4, 4, 4]
1: [0, 4]
0: [4, 3]

Lift Stops at 0 - [4, 3] in the lift
Lift Stops at 1 - [4, 3, 4] in the lift (queue at floor 1: [0])
Lift Stops at 2 - [4, 3, 4, 3] in the lift (queue at floor 2: [4, 4, 4])
Lift Stops at 3 - [4, 4, 4, 4] in the lift (queue at floor 3: [1, 0])
Lift Stops at 4 - [2] in the lift (queue at floor 4: [])
Lift Stops at 3 - [2, 1, 0] in the lift (queue at floor 3: [])
Lift Stops at 2 - [1, 0] in the lift (queue at floor 2: [4, 4, 4])
Lift Stops at 1 - [0, 0] in the lift (queue at floor 1: [])
Lift Stops at 0 - [] in the lift (queue at floor 0: [])
Lift Stops at 2 - [4, 4, 4] in the lift (queue at floor 2: [])
************* WHY IS IT SUPPOSE TO STOP AT FLOOR 3 HERE ****************
Lift Stops at 4 - [] in the lift (queue at floor 4: [])
Lift Stops at 0 - [] in the lift (queue at floor 4: [])

Can someone tell me why my logic above is wrong. I'm going crazy on this