aising2019C
C - Alternating Path
https://gyazo.com/6eb7e020e386120d4b5fa5a5331e74af
Thoughts.
When adjacent squares are of different colors, they are good walls to pass through.
This relationship is symmetric
That is, the connected component of an undirected graph
UnionFind then triangle number
A kind of Frequency→Triangular number.
Official Explanation
Missed the "black and white pair."
I thought it was two arbitrary points.
Black x white" instead of triangular numbers
aising2019
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