You wish to enter a whole number onto your simple four-function calculator. Unfortunately for you, some of the keys are broken. Nonetheless, rather than buy a new calculator, you enjoy the challenge presented before you.
Your calculator is a very primitive one, and can only display positive numbers with up to three digits. Initially, your display does not show anything, until you press a number key. Any time an operation exceeds the number 999, it causes an error, and you cannot continue.
You are given int keys, indicating which numeric keys are still functional, and String operators indicating which of the four operators are available to you. Assume that the equals key is always available. Finally, you are given int target, indicating the number you wish to display.
When you perform a division, your calculator performs an integer division, dropping any remainder. Thus, pressing "23/7=" yields 3, and "3/8" yields 0. Pressing the equals key completes any calculation, and any subsequent key presses after pressing equals discards the current display, and starts a new calculation.
You are to return an int indicating the minimum number of key presses necessary to display the target number. If it is not possible to ever get your display to show the target number, return -1.