Reducing into map in two steps not equivalent to combining steps

Questions / Help
1

Can someone explain why expand_map and expand_map2 are not equivalent below? Since the Map.put/3 call is being called with distinct keys, I can’t see why they should be different.

defmodule Day16Weirdness do
  def expand_map(map, width, height) do
    map
    |> Enum.reduce(map, fn {{r, c}, risk}, map ->
      1..4
      |> Enum.reduce(map, fn i, map ->
        Map.put(map, {r + i * width, c}, increment_risk(risk, i))
      end)
    end)
    |> Enum.reduce(map, fn {{r, c}, risk}, map ->
      1..4
      |> Enum.reduce(map, fn i, map ->
        Map.put(map, {r, c + i * height}, increment_risk(risk, i))
      end)
    end)
  end

  def expand_map2(map, width, height) do
    map
    |> Enum.reduce(map, fn {{r, c}, risk}, map ->
      1..4
      |> Enum.reduce(map, fn i, map ->
        Map.put(map, {r + i * width, c}, increment_risk(risk, i))
        |> Map.put({r, c + i * height}, increment_risk(risk, i))
      end)
    end)
  end

  defp increment_risk(risk, i) do 
    x = risk + i
    if x > 9 do 
      x - 9
    else 
      x
    end
  end
end
##############
map = for r <- 0..4,
c <- 0..4 do 
  {r,c} 
end
|> Enum.zip(1..25 |> Enum.map(&rem(&1, 10)))
|> Enum.into(%{})

new_map = expand_map(map, 5, 5) |> IO.inspect(limit: :infinity)
new_map2 = expand_map2(map, 5, 5) |> IO.inspect(limit: :infinity)
(new_map == new_map2) |> IO.inspect()

Here’s the output:

Summary

This text will be hidden

%{
  {4, 5} => 2,
  {19, 22} => 1,
  {16, 10} => 2,
  {11, 8} => 3,
  {11, 19} => 5,
  {16, 24} => 7,
  {6, 18} => 4,
  {17, 11} => 7,
  {15, 17} => 9,
  {17, 7} => 7,
  {10, 13} => 8,
  {5, 9} => 7,
  {12, 16} => 7,
  {14, 16} => 7,
  {6, 23} => 5,
  {17, 22} => 1,
  {10, 19} => 1,
  {14, 15} => 6,
  {3, 15} => 9,
  {14, 17} => 8,
  {13, 6} => 1,
  {4, 19} => 8,
  {12, 8} => 7,
  {5, 17} => 7,
  {3, 16} => 1,
  {23, 8} => 5,
  {5, 22} => 8,
  {1, 2} => 8,
  {16, 15} => 3,
  {15, 16} => 8,
  {8, 5} => 8,
  {1, 24} => 4,
  {23, 23} => 8,
  {18, 10} => 2,
  {4, 15} => 4,
  {14, 24} => 2,
  {4, 18} => 7,
  {21, 24} => 8,
  {24, 15} => 8,
  {14, 8} => 7,
  {6, 21} => 3,
  {3, 18} => 3,
  {0, 9} => 6,
  {10, 23} => 1,
  {7, 17} => 7,
  {8, 6} => 9,
  {24, 23} => 3,
  {13, 22} => 5,
  {23, 24} => 8,
  {8, 11} => 1,
  {15, 8} => 8,
  {24, 9} => 1,
  {8, 10} => 9,
  {3, 6} => 8,
  {2, 16} => 5,
  {16, 23} => 7,
  {3, 17} => 2,
  {6, 24} => 5,
  {3, 12} => 1,
  {6, 15} => 1,
  {7, 16} => 6,
  {2, 4} => 5,
  {8, 17} => 3,
  {16, 18} => 6,
  {18, 23} => 7,
  {19, 7} => 7,
  {4, 8} => 5,
  {24, 13} => 1,
  {17, 16} => 8,
  {16, 8} => 4,
  {4, 12} => 5,
  {23, 21} => 6,
  {24, 21} => 1,
  {23, 14} => 6,
  {13, 13} => 4,
  {19, 16} => 8,
  {24, 16} => 9,
  {10, 5} => 4,
  {6, 5} => 8,
  {20, 21} => 1,
  {17, 24} => 3,
  {18, 24} => 7,
  {19, 12} => 8,
  {21, 19} => 7,
  {18, 22} => 6,
  {13, 12} => 3,
  {8, 14} => 3,
  {15, 18} => 1,
  {12, 17} => 8,
  {19, 10} => 6,
  {21, 21} => 6,
  {8, 22} => 4,
  {18, 5} => 1,
  {0, 3} => 4,
  {1, 1} => 7,
  {9, 11} => 5,
  {2, 20} => 5,
  {13, 20} => 3,
  {5, 23} => 9,
  {17, 18} => 1,
  {9, 6} => 4,
  {11, 22} => 5,
  {20, 7} => 8,
  {4, 3} => 4,
  {1, 22} => 3,
  {14, 5} => 4,
  {17, 23} => 2,
  {24, 12} => 9,
  {13, 23} => 6,
  {3, 7} => 9,
  {9, 13} => 7,
  {13, 10} => 1,
  {15, 14} => 1,
  {22, 8} => 9,
  {19, 8} => 8,
  {5, 10} => 4,
  {0, 5} => 2,
  {22, 17} => 1,
  {6, 10} => 9,
  {0, 1} => 2,
  {18, 21} => 5,
  {1, 16} => 1,
  {20, 5} => 6,
  {8, 9} => 2,
  {8, 19} => 4,
  {20, 22} => 2,
  {8, 20} => 2,
  {21, 12} => 5,
  {21, 20} => 5,
  {4, 0} => 1,
  {3, 14} => 2,
  {7, 19} => 9,
  {3, 2} => 8,
  {8, 24} => 5,
  {19, 6} => 6,
  {9, 8} => 6,
  {2, 21} => 6,
  {24, 14} => 2,
  {14, 19} => 1,
  {2, 13} => 6,
  {7, 9} => 7,
  {24, 20} => 9,
  {24, 10} => 7,
  {0, 8} => 5,
  {7, 15} => 5,
  {22, 12} => 9,
  {9, 18} => 8,
  {7, 21} => 7,
  {12, 10} => 5,
  {4, 20} => 5,
  {11, 5} => 9,
  {4, 13} => 6,
  {3, 1} => 7,
  {24, 19} => 3,
  {5, 16} => 6,
  {3, 23} => 4,
  {21, 18} => 7,
  {10, 20} => 7,
  {22, 24} => 4,
  {2, 0} => 1,
  {21, 5} => 2,
  {10, 17} => 8,
  {10, 16} => 7,
  {19, 18} => 1,
  {15, 12} => 8,
  {12, 13} => 8,
  {17, 17} => 9,
  {19, 11} => 7,
  {21, 10} => 3,
  {21, 16} => 5,
  {15, 15} => 7,
  {10, 8} => 7,
  {2, 11} => 4,
  {11, 23} => 6,
  {11, 24} => 6,
  {8, 12} => 2,
  {19, 20} => 8,
  {12, 15} => 6,
  {22, 11} => 8,
  {15, 10} => 6,
  {7, 18} => 8,
  {2, 7} => 4,
  {4, 6} => 3,
  {19, 5} => 5,
  {21, 22} => 7,
  {12, 23} => 1,
  {15, 6} => 6,
  {21, 17} => 6,
  {19, 9} => 9,
  {16, 20} => 4,
  {6, 17} => 3,
  {23, 9} => 5,
  {17, 5} => 5,
  {13, 21} => 4,
  {17, 10} => 6,
  {6, 20} => 2,
  {0, 7} => 4,
  {0, 16} => 5,
  {10, 15} => 6,
  {17, 14} => 1,
  {9, 20} => 6,
  {5, 20} => 6,
  {24, 11} => 8,
  {4, 23} => 8,
  {21, 9} => 5,
  {8, 23} => 5,
  {2, 10} => 3,
  {3, 11} => 9,
  {18, 11} => 3,
  {4, 11} => 4,
  {2, 22} => 7,
  {4, 10} => 3,
  {9, 19} => 9,
  {7, 23} => 9,
  {15, 11} => 7,
  {0, 0} => 1,
  {8, 7} => 1,
  {14, 10} => 5,
  {5, 8} => 6,
  {7, 6} => 4,
  {3, 20} => 1,
  {0, 10} => 3,
  {17, 12} => 8,
  {22, 15} => 8,
  {18, 20} => 4,
  {22, 10} => 7,
  {19, 23} => 2,
  {2, 8} => 5,
  {19, 19} => 2,
  {1, 4} => 0,
  {23, 6} => 3,
  {10, 6} => 5,
  {14, 18} => 9,
  {22, 22} => 2,
  {22, 9} => 1,
  {9, 21} => 7,
  {12, 18} => 9,
  {11, 14} => 4,
  {6, 19} => 4,
  {9, 22} => 8,
  {20, 8} => 9,
  {2, 17} => 6,
  {12, 7} => 6,
  {18, 14} => 5,
  {5, 6} => 4,
  {22, 21} => 1,
  {9, 5} => 3,
  {1, 11} => 9,
  {7, 22} => 8,
  {20, 10} => 7,
  {6, 6} => 9,
  {17, 15} => 7,
  {23, 18} => 7,
  {5, 11} => 5,
  {12, 19} => 1,
  {4, 14} => 7,
  {17, 6} => 6,
  {20, 23} => 3,
  {14, 20} => 7,
  {0, 4} => 5,
  {21, 6} => 3,
  {22, 13} => 1,
  {5, 19} => 9,
  {9, 16} => 6,
  {13, 24} => 6,
  {6, 8} => 2,
  {1, 7} => 9,
  {4, 2} => 3,
  {13, 15} => 2,
  {15, 9} => 9,
  {24, 18} => 2,
  {24, 24} => 4,
  {13, 8} => 3,
  {15, 7} => 7,
  {2, 19} => 8,
  {1, 19} => 3,
  {13, 18} => 5,
  {22, 18} => 2,
  {22, 23} => 3,
  {8, 8} => 2,
  {2, 15} => 4,
  {13, 9} => 3,
  {11, 12} => 3,
  {22, 20} => 9,
  {2, 3} => 4,
  {2, 23} => 8,
  {16, 14} => 5,
  {17, 21} => 9,
  {18, 9} => 4,
  {16, 17} => 5,
  {15, 5} => 5,
  {23, 12} => 5,
  {13, 17} => 4,
  {1, 8} => 1,
  {12, 5} => 4,
  {11, 10} => 1,
  {20, 13} => 1,
  {16, 19} => 6,
  {15, 23} => 2,
  {3, 4} => 0,
  {10, 21} => 8,
  {12, 22} => 9,
  {23, 13} => 6,
  {20, 19} => 3,
  {10, 24} => 2,
  {21, 13} => 6,
  {17, 8} => 8,
  {7, 5} => 3,
  {19, 14} => 1,
  {15, 19} => 2,
  {16, 5} => 1,
  {1, 23} => 4,
  {9, 24} => 1,
  {23, 11} => 4,
  {17, 13} => 9,
  {23, 10} => 3,
  {14, 13} => 8,
  {1, 15} => 9,
  {11, 7} => 2,
  {18, 6} => 2,
  {22, 7} => 8,
  {24, 6} => 7,
  {11, 9} => 3,
  {23, 22} => 7,
  {14, 9} => 8,
  {2, 1} => 2,
  {24, 8} => 9,
  {4, 16} => 5,
  {3, 19} => 3,
  {23, 20} => 5,
  {5, 13} => 7,
  {11, 17} => 4,
  {3, 10} => 8,
  {14, 11} => 6,
  {3, 22} => 3,
  {1, 14} => 2,
  {7, 8} => 6,
  {0, 21} => 6,
  {22, 14} => 2,
  {14, 23} => 1,
  {9, 14} => 8,
  {18, 19} => 6,
  {4, 7} => 4,
  {14, 14} => 9,
  {12, 12} => 7,
  {1, 21} => 2,
  {23, 16} => 5,
  {20, 6} => 7,
  {11, 20} => 3,
  {3, 3} => 9,
  {20, 11} => 8,
  {13, 7} => 2,
  {21, 8} => 5,
  {23, 15} => 4,
  {1, 10} => 8,
  {13, 5} => 9,
  {10, 9} => 8,
  {3, 0} => 6,
  {21, 11} => 4,
  {6, 14} => 3,
  {20, 18} => 2,
  {4, 21} => 6,
  {7, 11} => 5,
  {4, 9} => 6,
  {9, 15} => 5,
  {6, 13} => 3,
  {24, 22} => 2,
  {10, 7} => 6,
  {22, 19} => 3,
  {16, 16} => 4,
  {17, 9} => 9,
  {12, 20} => 7,
  {7, 20} => 6,
  {11, 6} => 1,
  {11, 21} => 4,
  {20, 17} => 1,
  {6, 16} => 2,
  {13, 14} => 4,
  {11, 16} => 3,
  {7, 7} => 5,
  {10, 12} => 7,
  {0, 17} => 6,
  {20, 16} => 9,
  {15, 24} => 3,
  {10, 14} => 9,
  {14, 6} => 5,
  {19, 13} => 9,
  {6, 22} => 4,
  {16, 6} => 2,
  {17, 20} => 8,
  {11, 18} => 5,
  {2, 24} => 9,
  {16, 7} => 3,
  {8, 16} => 2,
  {14, 7} => 6,
  {10, 10} => 5,
  {9, 10} => 4,
  {14, 21} => 8,
  {19, 24} => 3,
  {18, 18} => 6,
  {20, 9} => 1,
  {20, 20} => 9,
  {8, 13} => 3,
  {18, 16} => 4,
  {21, 14} => 6,
  {8, 18} => 4,
  {20, 24} => 4,
  {0, 19} => 8,
  {1, 6} => 8,
  {4, 1} => 2,
  {5, 21} => 7,
  {18, 12} => 4,
  {5, 5} => 3,
  {6, 12} => 2,
  {5, 14} => 8,
  {7, 14} => 8,
  {7, 12} => 6,
  {16, 22} => 6,
  {15, 22} => 1,
  {18, 17} => 5,
  {1, 9} => 1,
  {21, 15} => 4,
  {4, 24} => 9,
  {8, 21} => 3,
  {13, 16} => 3,
  {0, 22} => 7,
  {1, 12} => 1,
  {22, 6} => 7,
  {9, 23} => 9,
  {16, 13} => 5,
  {16, 11} => 3,
  {19, 17} => 9,
  {12, 24} => 2,
  {19, 21} => 9,
  {1, 17} => 2,
  {12, 6} => 5,
  {5, 24} => 1,
  {3, 5} => 7,
  {0, 24} => 9,
  {1, 0} => 6,
  {2, 14} => 7,
  {5, 18} => 8,
  {3, 13} => 2,
  {0, 15} => 4,
  {0, 11} => 4,
  {23, 5} => 2,
  {1, 13} => 2,
  {11, 15} => 2,
  {4, 22} => 7,
  {2, 6} => 3,
  {12, 9} => 8,
  {21, 7} => 4,
  {1, 5} => 7,
  {23, 17} => 6,
  {14, 22} => 9,
  {15, 13} => 9,
  {7, 24} => 1,
  {18, 8} => 4,
  {2, 12} => 5,
  {21, 23} => 8,
  {1, 18} => 3,
  {20, 14} => 2,
  {13, 19} => 5,
  {9, 7} => 5,
  {7, 10} => 4,
  {12, 14} => 9,
  {24, 5} => 6,
  {24, 17} => 1,
  {23, 19} => 7,
  {2, 18} => 7,
  {15, 20} => 8,
  {6, 11} => 1,
  {2, 5} => 2,
  {15, 21} => 9,
  {13, 11} => 2,
  {0, 20} => 5,
  {0, 13} => 6,
  {18, 7} => 3,
  {12, 11} => 6,
  {8, 15} => 1,
  {2, 2} => 3,
  {5, 7} => 5,
  {6, 9} => 2,
  {0, 2} => 3,
  {22, 16} => 9,
  {18, 15} => 3,
  {9, 12} => 6,
  {4, 4} => 5,
  {22, 5} => 6,
  {0, 6} => 3,
  {16, 21} => 5,
  {6, 7} => 1,
  {10, 11} => 6,
  {0, 12} => 5,
  {3, 8} => 1,
  {3, 24} => 4,
  {11, 13} => 4,
  {17, 19} => 2,
  {10, 22} => 9,
  {0, 18} => 7,
  {9, 17} => 7,
  {5, 12} => 6,
  {12, 21} => 8,
  {19, 15} => 7,
  {14, 12} => 7,
  {0, 14} => 7,
  {7, 13} => 7,
  {0, 23} => 8,
  {16, 9} => 4,
  {16, 12} => 4,
  {11, 11} => 2,
  {20, 15} => 8,
  {4, 17} => 6,
  {18, 13} => 5,
  {1, 3} => 9,
  {1, 20} => 1,
  {9, 9} => 7,
  {3, 9} => 1,
  {5, 15} => 5,
  {24, 7} => 8,
  {20, 12} => 9,
  {2, 9} => 6,
  {3, 21} => 2,
  {10, 18} => 9,
  {23, 7} => 4
}
%{
  {4, 5} => 2,
  {20, 3} => 8,
  {17, 0} => 4,
  {3, 15} => 9,
  {4, 19} => 8,
  {3, 16} => 1,
  {15, 3} => 7,
  {1, 2} => 8,
  {15, 2} => 6,
  {1, 24} => 4,
  {4, 15} => 4,
  {4, 18} => 7,
  {12, 3} => 6,
  {3, 18} => 3,
  {0, 9} => 6,
  {16, 1} => 1,
  {18, 3} => 3,
  {10, 0} => 3,
  {5, 2} => 4,
  {3, 6} => 8,
  {2, 16} => 5,
  {3, 17} => 2,
  {12, 1} => 4,
  {3, 12} => 1,
  {2, 4} => 5,
  {24, 1} => 6,
  {4, 8} => 5,
  {19, 1} => 5,
  {11, 2} => 1,
  {4, 12} => 5,
  {24, 2} => 7,
  {22, 1} => 6,
  {14, 3} => 6,
  {0, 3} => 4,
  {1, 1} => 7,
  {2, 20} => 5,
  {22, 4} => 9,
  {4, 3} => 4,
  {1, 22} => 3,
  {3, 7} => 9,
  {16, 2} => 2,
  {13, 2} => 1,
  {5, 0} => 2,
  {11, 3} => 2,
  {0, 5} => 2,
  {0, 1} => 2,
  {1, 16} => 1,
  {24, 0} => 5,
  {4, 0} => 1,
  {13, 1} => 9,
  {17, 4} => 8,
  {3, 14} => 2,
  {3, 2} => 8,
  {21, 4} => 4,
  {10, 3} => 6,
  {2, 21} => 6,
  {8, 1} => 8,
  {2, 13} => 6,
  {7, 3} => 5,
  {0, 8} => 5,
  {4, 20} => 5,
  {4, 13} => 6,
  {3, 1} => 7,
  {16, 4} => 3,
  {6, 1} => 8,
  {17, 3} => 7,
  {3, 23} => 4,
  {2, 0} => 1,
  {2, 11} => 4,
  {8, 3} => 1,
  {8, 4} => 1,
  {23, 1} => 2,
  {2, 7} => 4,
  {4, 6} => 3,
  {23, 2} => 3,
  {9, 4} => 6,
  {22, 2} => 7,
  {6, 2} => 9,
  {23, 3} => 4,
  {0, 7} => 4,
  {0, 16} => 5,
  {9, 0} => 2,
  {4, 23} => 8,
  {7, 2} => 4,
  {2, 10} => 3,
  {3, 11} => 9,
  {4, 11} => 4,
  {2, 22} => 7,
  {4, 10} => 3,
  {0, 0} => 1,
  {12, 4} => 7,
  {3, 20} => 1,
  {23, 0} => 1,
  {0, 10} => 3,
  {17, 2} => 6,
  {18, 0} => 9,
  {2, 8} => 5,
  {1, 4} => 0,
  {18, 2} => 2,
  {2, 17} => 6,
  {19, 4} => 8,
  {1, 11} => 9,
  {4, 14} => 7,
  {9, 3} => 5,
  {0, 4} => 5,
  {21, 0} => 1,
  {1, 7} => 9,
  {4, 2} => 3,
  {2, 19} => 8,
  {1, 19} => 3,
  {23, 4} => 4,
  {2, 15} => 4,
  {2, 3} => 4,
  {2, 23} => 8,
  {11, 1} => 9,
  {1, 8} => 1,
  {10, 4} => 7,
  {8, 2} => 9,
  {24, 4} => 9,
  {3, 4} => 0,
  {14, 1} => 4,
  {20, 0} => 5,
  {18, 1} => 1,
  {1, 23} => 4,
  {12, 2} => 5,
  {1, 15} => 9,
  {2, 1} => 2,
  {15, 1} => 5,
  {4, 16} => 5,
  {3, 19} => 3,
  {7, 0} => 2,
  {11, 0} => 8,
  {3, 10} => 8,
  {3, 22} => 3,
  {1, 14} => 2,
  {0, 21} => 6,
  {20, 2} => 7,
  {4, 7} => 4,
  {1, 21} => 2,
  {3, 3} => 9,
  {1, 10} => 8,
  {21, 3} => 4,
  {3, 0} => 6,
  {4, 21} => 6,
  {17, 1} => 5,
  {4, 9} => 6,
  {9, 1} => 3,
  {0, 17} => 6,
  {13, 4} => 2,
  {20, 4} => 9,
  {11, 4} => 2,
  {6, 0} => 7,
  {2, 24} => 9,
  {7, 1} => 3,
  {22, 0} => 5,
  {5, 3} => 5,
  {15, 4} => 8,
  {0, 19} => 8,
  {1, 6} => 8,
  {4, 1} => 2,
  {21, 1} => 2,
  {8, 0} => 7,
  {1, 9} => 1,
  {4, 24} => 9,
  {0, 22} => 7,
  {1, 12} => 1,
  {9, 2} => 4,
  {19, 0} => 4,
  {10, 1} => 4,
  {6, 4} => 1,
  {1, 17} => 2,
  {3, 5} => 7,
  {18, 4} => 3,
  {0, 24} => 9,
  {1, 0} => 6,
  {2, 14} => 7,
  {13, 0} => 8,
  {3, 13} => 2,
  {0, 15} => 4,
  {0, 11} => 4,
  {16, 0} => 9,
  {1, 13} => 2,
  {4, 22} => 7,
  {2, 6} => 3,
  {1, 5} => 7,
  {19, 2} => 6,
  {2, 12} => 5,
  {12, 0} => 3,
  {13, 3} => 2,
  {1, 18} => 3,
  {20, 1} => 6,
  {19, 3} => 7,
  {16, 3} => 3,
  {21, 2} => 3,
  {5, 1} => 3,
  {14, 0} => 3,
  {2, 18} => 7,
  {2, 5} => 2,
  {0, 20} => 5,
  {10, 2} => 5,
  {0, 13} => 6,
  {24, 3} => 8,
  {2, 2} => 3,
  {14, 2} => 5,
  {0, 2} => 3,
  {4, 4} => 5,
  {7, 4} => 6,
  {0, 6} => 3,
  {0, 12} => 5,
  {3, 8} => 1,
  {3, 24} => 4,
  {14, 4} => 7,
  {0, 18} => 7,
  {6, 3} => 1,
  {0, 14} => 7,
  {0, 23} => 8,
  {15, 0} => 4,
  {5, 4} => 6,
  {22, 3} => 8,
  {4, 17} => 6,
  {1, 3} => 9,
  {1, 20} => 1,
  {3, 9} => 1,
  {2, 9} => 6,
  {3, 21} => 2
}
false
1 Like
2

You should no be using the same variable name for everything, as you will totally loose track of what is going on with your code.

for your first expand, map is your enumerable, your accumulator, then you pipe again on it but your accumulator is your original map so you loose everything from the first reduce, but the numbers elements added is the total number of elements from the result of the first reduce.

4 Likes
3

Here’s a rewrite of your code.
expand_map is not the same as your original as there were some stuff that didn’t make any sense… I tried to correct, like the second reduce is:
Enum.reduce(result1, result1, ... where in your original code you were doing Enum.reduce(result1, map, ...

I hope you can see why expand_map and expand_map2 are totally different.

defmodule Day16Weirdness do
  def expand_map(map, width, height) do
    result1 =
      Enum.reduce(map, map, fn {{r, c}, risk}, acc1 ->
        Enum.reduce(1..4, acc1, fn i, acc2 ->
          Map.put(acc2, {r + i * width, c}, increment_risk(risk, i))
        end)
      end)

    result2 =
      Enum.reduce(result1, result1, fn {{r, c}, risk}, acc1 ->
        Enum.reduce(1..4, acc1, fn i, acc2 ->
          Map.put(acc2, {r, c + i * height}, increment_risk(risk, i))
        end)
      end)

    result2
  end

  def expand_map2(map, width, height) do
    Enum.reduce(map, map, fn {{r, c}, risk}, acc1 ->
      Enum.reduce(1..4, acc1, fn i, acc2 ->
        acc2
        |> Map.put({r + i * width, c}, increment_risk(risk, i))
        |> Map.put({r, c + i * height}, increment_risk(risk, i))
      end)
    end)
  end

  defp increment_risk(risk, i) do
    x = risk + i

    if x > 9 do
      x - 9
    else
      x
    end
  end
end
3 Likes