patterns possible on 3x3 matrix of numbers
Possible Duplicate:
android lock password combinations
Respected sir, I came across a question which asked for finding all the unique pattern possible given a 3x3 matrix with numbers from 1-9. which is same as android lock screen. Can you help me how to find it ?? I was thinking can we use floyd warshall for this and increment count whenever the value changes in the subsequent matrix??
Answer
Combinations of the Android pattern lock screen would not be from 1-9. Instead, they would be 4-9, as the lock pattern needs a minimum of four inputs, and anything below that is invalid (at least 2.3 onwards. I believe 2.2 and below allowed 3 point locks). Here's the breakdown of the combinations:
Moves = 4, combinations = 1624
Moves = 5, combinations = 7152
Moves = 6, combinations = 26016
Moves = 7, combinations = 72912
Moves = 8, combinations = 140704
Moves = 9, combinations = 140704
Total possibilities: 1624 + 7152 + 26016 + 72912 + 140704 + 140704 = 389112
A complete breakdown of the Math behind this given by a Google Engineer can be found here.