Placing + and - signs in a 4 × 4 square
Source: Tournament of Towns Spring 2003 - Senior A-Level - Problem 6
June 15, 2011
combinatorics unsolvedcombinatorics
Problem Statement
The signs "" or "" are placed in all cells of a square table. It is allowed to change a sign of any cell altogether with signs of all its adjacent cells (i.e. cells having a common side with it). Find the number of different tables that could be obtained by iterating this procedure.