There are 16 buttons in a four by four array. Each button has a horizontal arrow, pointing left or right, and a vertical arrow, pointing up or down. Initially, all arrows point towards the center of the array. In the below diagram, U is up, D is down, R is right, and L is left.

DR DR DL DL
DR DR DL DL
UR UR UL UL
UR UR UL UL

When you press a button, all other buttons in the direction of its horizontal arrow flip their vertical arrows, while all other buttons in the direction of the vertical arrow flip their horizontal arrows. The following diagram is the result after pressing the button in the upper left corner.

DR UR UL UL
DL DR DL DL
UL UR UL UL
UL UR UL UL

Find the least number of button presses required to get to the position in which all arrows point away from the center of the array.

(In reply to Flip by brianjn)

Actually, I wrote a java program for this, but I don't have the ability to post it up here, and I don't have the connections to make a cell phone game out of it.

I also experimented with a variation of this, where the other arrow in each button changed, but I like this rule better.

Posted by Tristan on 2006-10-30 13:11:28