You can keep doing the same puzzle to get this.
Start a new game. Open the door with code 1,2,3,4
After you open the door, Save. There's two easy puzzles you can get after.
Open the next door with 1,5,1,3,2,4
Grab the gold key in that room and open the next door with it.
After doing both you can quit out and load save and repeat.
You can see me do it in my walkthrough video: