This is a Minecraft combination lock that is 100% customizable!
Step 1: Buttons
Create a row of as many buttons as you want with redstone behind them.
Step 2: Mechanism
Make a row of pistons corresponding to the amount of digits with sand on top and a redstone torch that leads to a repeater then alternates leaving a space for the pistons to extend.
Step 3: Combination
Make a line of redstone from your chosen combination's buttons that lead to it's corresponding piston in the digit.
EX: 1 is 1st so it leads to piston 1. 5 is 2nd so it leads to piston 2. Etc.
Step 4: Resetting
Make a line of redstone that connects all not chosen numbers to turn off the redstone torch.
Step 5: Output
Create a line of redstone that connects the repeater after the last piston to your mechanism of choice (Door in this case) and to the beginning redstone torch, turning it off. Do not just do that, though. Add a pulse extender to keep the ending mechanism on longer.