DIY: Open Lock

Problem statement

You have an old lock in front of you with four circular wheels. Each wheel has ten slots: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. The wheels can rotate freely and wrap around. For example, we can turn '9' to be '0' or '0' to be '9'. Each move consists of turning one wheel one slot. Initially, the lock starts at '0000', a ...