# Bullet Drop™ #1

## Concept

Here is a basic example grid:

 AB
1\/
2\/
××


The player must first modify the grid by switching the slashes \ and / in as few moves as possible.

They then drop a bullet • from their chosen letter with the intention of reaching a target × at the bottom.

As the bullet drops, if it hits a \ it will bounce right, and if it hits a / it will bounce left.

When the bullet moves horizontally, it must hit the same slash character it just hit in order to travel downwards.

If it hits the opposite slash character it will bounce back, causing an infinite loop. If it hits no slash, it will fall off the grid.

An answer to the example above might be:

2 moves: B1 A2 - drop from A

This example answer would result in:

 AB
1\\
2//
•×


## Challenge

Using my Super-Advanced Randomiser (my 9 year old son), here's the first ever Bullet Drop™ challenge:

 ABCDEFGHI
1/\\/\\///
2\\/\//\/\
3\//\/\\//
4/\/\\//\\
5///\\\///
6\\////\\\
7/\\//\//\
8///\\\///
9\\\/\/\\\
×××××××××


The minimum on this grid is

two moves:

if you first think of this problem but the ball can also bounce upward (lets call it a laser and mirrors problem), you can color the grid to see closed parts :

Then, you see that the easiest way is the blue, then any of the light blue, it is the only 1 move "laser & mirrors" winning configuration,

So then it's a bullet and can't move upwards, only the blue path could make this possible in 1 move, but you can see the traps in DE3 and BC4 that takes one or two more moves to complete (here 1 : D3) so the minimal is 2 moves (the one from the "laser" game, and the one to avoid the two traps)

But this does not prove us it is the only answer :

H2 I7 drop from I is also a valid answer, and coloring the grid helps i think.

You can solve it in

2 moves.

You flip

D3 and F9

and drop from

E.

• Yep. I wonder if it's possible in fewer moves? And are spoilers recommended for this type of challenge? Sep 3, 2017 at 20:36