Approach

Written by Isaiah Iliffe from CSESoc Education

A very short solution involves keeping track of $x$, the number Joseph's finger is currently over, initially 1, and treating each character as follows:

• L: decrement $x$ by 1.
• R: increment $x$ by 1.
• U: decrement $x$ by 3.
• D: increment $x$ by 3.
• P: print the digit $x$.

Alternatively, a 2D array representing the keypad will do the trick.