Edit: Nevermind, I realized I misread a detail in the original problem. Bother!
]]>Now we can move another left frog into the space, but that would get us back to the dead end that we already rejected, so we're left with //\/o\\.
And then it starts to get a little tricky, because we now have more than one option that has options coming off it. The main thing you need to watch out for is to make sure you don't make any //\\ groups.
]]>Apparently after the first step the positions could be
either //_/\\\ or /_//\\\
for convenience, let us use o instead of _ to express the empty space.
It may take you some tries though.
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