Make a two-dimensional array into a sequence of coordinates

[$f:(x,y)\to \{0,1\}[$ {(x, y) | f(x, y) = 1}

Advantages

• Rotation implementation available

• The process in its original form is O(N^2) with width N, but advantageous when $M:=\sum f$ is asymptotically smaller than that

• problem transformation

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