Doors & Locks $1.99 -> $0.99 USD iTunes Link: https://itunes.apple.com/us/app/doors-locks/id1159517006?mt=8
Pick it up while it's on sale I highly recommend this game and it's on sale! I'm certain you will enjoy the game. I paid more than the sale price and totally love playing it. Some of my friends are playing and say it's one of their favorites. If you play it to reach new levels you'll find that you can progress quickly through many levels which is fun. But at the higher levels, it can be super challenging for even the smartest folks. One tip, is to think of the game as somewhat Sudoku-like and feel free to stay on levels that challenge you. I'm on Masters but enjoy playing Skilled levels for a quick challenge. If you play it enough, you'll find a nice randomizer for coloring the doors once a person reaches 200 puzzles. Enjoy!