Day 239

[vaskoz]

Good morning! Here's your coding interview problem for today.

This problem was asked by Uber.

One way to unlock an Android phone is through a pattern of swipes across a 1-9 keypad.

For a pattern to be valid, it must satisfy the following:

All of its keys must be distinct.
It must not connect two keys by jumping over a third key, unless that key has already been used.
For example, 4 - 2 - 1 - 7 is a valid pattern, whereas 2 - 1 - 7 is not.

Find the total number of valid unlock patterns of length N, where 1 <= N <= 9.

[vaskoz]

389112 distinct patterns appear to be confirmed. https://www.quora.com/How-many-different-numbers-of-pattern-locks-can-be-made-on-an-Android-mobile-phone