Try it online (Thanks Dennis!)
Input for Windows: F_⌠1234567890
Input on Linux based system using ISO-8559-1: F_ô1234567890
Reasoning: I will be backThe heart of how the Malbolge program worked is that it depended on a behavior of the Malbolge interpreter which causes an infinite loop if it encounters any instruction which is not between 33 and 126. The program was constructed such that your input would allow you to explain this, maybemodify a single instruction.
Note: I couldn't getmodified the online interpreter to stop with this input, but I tested by buildingdump the interpreter with VS2017. This seemsprogram memory state at the beginning of execution and to also produce 'normalized' source code which takes the form of a list of op codes that will be what DoorKnob used to test it, sorun during the execution of the program. With that is also what I usedinformation you could (slowly) determine that even though the program took 13 inputs only the 1st and 3rd inputs actually mattered.
Edit: AddedLooking through the inputnormalized code and memory dump (and a touch of debugger help) I used on my raspberry pi to getdevised the following:
a = op(input 1, 29524)
b = op(input 3, a)
c = op(486, b)
d = op(c, 37)
e = d/4 + d%3 * 3^9
e must be between 33 and 126
Where op is the so called tritwise "op" that is described in the specification. Using this haltinformation you can write a simple program which iterates over the possible inputs (0 to 255) and finds all solutions which meet the above criteria. Looks like I was running into an encoding issuehad found 2219 possible solutions, some of which will probably not be working solutions (you can't input the required characters). Specifically the above inputs are based on the solution:
(Input 1 = 70, Input 3 = 244)