No.1 array series solution ideas
A for loop resolves.
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No.2 Different gyronic subsequences of length 3
Their thinking
There are at most 26 * 26 gyrotext subsequences of length 3, and the existence of each seed sequence can be judged in turn.
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No.3 paints the mesh with three different colors
Their thinking
By pressing DP, each column can be compressed into a number between 0 and 242 (equivalent to the representation in base 3).
Define state dpi to represent the number of schemes in column I when the coloring condition of column I is j.
Dpi = SUM(dpi – 1) if valid(j) and valid(k) and valid(j, k)
In the equation, valid(j) means that j itself is a valid coloring (no adjacent columns of the same color), and valid(j, k) means that it is valid to coloring j and k as adjacent columns.
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No.4 Merges multiple binary search trees
Their thinking
DFS is fine, see the notes for details.
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