#124
Analyze Reversi

 Difficulty: Hard Topics: game

Reversi is normally played on an 8 by 8 board. In this problem, a 4 by 4 board is represented as a two-dimensional vector with black, white, and empty pieces represented by 'b, 'w, and 'e, respectively. Create a function that accepts a game board and color as arguments, and returns a map of legal moves for that color. Each key should be the coordinates of a legal move, and its value a set of the coordinates of the pieces flipped by that move.

Board coordinates should be as in calls to get-in. For example, `[0 1]` is the topmost row, second column from the left.

 ```(= {[1 3] #{[1 2]}, [0 2] #{[1 2]}, [3 1] #{[2 1]}, [2 0] #{[2 1]}} (__ '[[e e e e] [e w b e] [e b w e] [e e e e]] 'w))``` ```(= {[3 2] #{[2 2]}, [3 0] #{[2 1]}, [1 0] #{[1 1]}} (__ '[[e e e e] [e w b e] [w w w e] [e e e e]] 'b))``` ```(= {[0 3] #{[1 2]}, [1 3] #{[1 2]}, [3 3] #{[2 2]}, [2 3] #{[2 2]}} (__ '[[e e e e] [e w b e] [w w b e] [e e b e]] 'w))``` ```(= {[0 3] #{[2 1] [1 2]}, [1 3] #{[1 2]}, [2 3] #{[2 1] [2 2]}} (__ '[[e e w e] [b b w e] [b w w e] [b w w w]] 'b)) ```

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