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PROJECT EULER · #0976

XO Game

Statement only · UnsolvedOriginal problem ↗

Two players X and O play a game with k strips of squares of lengths n1,,nk, originally all blank.

Starting with X, they make moves in turn. At X's turn, X draws an "X" symbol; at O's turn, O draws an "O" symbol.
The symbol must be drawn in one blank square with either red or blue pen, subject to the following restrictions:

  1. two symbols in adjacent squares on one strip must be different symbols and must have different colour;
  2. if there is at least one blank strip, then one must draw on a blank strip.

Whoever does not have a valid move loses the game.

Let P(K,N) be the number of tuples (n1,,nk) such that 1kK, 1n1nkN and that X has a winning strategy to the corresponding game.
For example, P(2,4)=7 and P(5,10)=901.

Find P(107,107)mod1234567891.

Write-up coming later

The complete problem is available here. An approach, code, and answer will be added later.