Pass in an index into a 2-dimensional square grid and get back a table containing the index of all neighbor squares.

getneighbors.lua

--==============================================================
-- pass in a lily pad number and get back a
-- table containing all the neighbors for
-- that lily pad.

local numCols = 11
local numRows = 7

local function getNeighbors(padNum)

  local neighbors = {}

  local function inLeftColumn()
    return ((padNum-1) % numCols) == 0
  end
  local function inRightColumn()
    return (padNum % numCols) == 0
  end

  local inLeft = inLeftColumn() 
  local inRight = inRightColumn()

  -- number above, above left/right
  if padNum > numCols then
    neighbors[#neighbors+1] = padNum - numCols
    if not inLeft then
      neighbors[#neighbors+1] = padNum - numCols - 1
    end
    if not inRight then
      neighbors[#neighbors+1] = padNum - numCols + 1
    end
  end

  -- number below & below left/right
  if padNum <= (numCols * (numRows-1)) then
    neighbors[#neighbors+1] = padNum + numCols -- number below
    if not inLeft then
      neighbors[#neighbors+1] = padNum + numCols - 1
    end
    if not inRight then
      neighbors[#neighbors+1] = padNum + numCols + 1
    end
  end

  -- number to right
  if not inRight then
    neighbors[#neighbors+1] = padNum + 1
  end

  -- number to left
  if not inLeft then
    neighbors[#neighbors+1] = padNum - 1
  end

  return neighbors
end